Hearing Loss Hearing Loss Workers have been using hearing protection devices (HPD) since the 1960's to protect themselves from high levels of noise. Approximately 30 million workers in the United States are occupationally exposed to hazardous noises each year. 10 million of those workers suffer from noise induced hearing loss (NIHL) according to NIOSH. For more than 25 years hearing loss has been listed as one of the most prevalent occupational health concerns. Permanent hearing loss can occur when exposed to high levels of noise. Repeated exposure to high levels of noise can cause tinnitus (ringing in the ears). Other issues related to loud noise at work are physical and psychological stress, reduction in concentration and communication, loss of productivity, and increased probability of work related accidents. With radically smart products, the right education, and a structured hearing conservation program noise-induced hearing loss is 100% preventable. 
snr snr Signal-to-noise ratiocollapse all in page Syntaxr = snr (x,y)r = snr (x)r = snr (x,fs,n)r = snr (pxx,f,'psd')r = snr (pxx,f,n,'psd')r = snr (sxx,f,rbw,'power')r = snr (sxx,f,rbw,n,'power')r = snr ( ___ ,'aliased') [r,noisepow] = snr ( ___)snr ( ___)Descriptionexampler = snr ( x, y) returns the signal-to-noise ratio (SNR) in decibels of a signal, x , by computing the ratio of its summed squared magnitude to that of the noise, y. y must have the same dimensions as x. Use this form when the input signal is not necessarily sinusoidal and you have an estimate of the noise.exampler = snr ( x) returns the SNR in decibels relative to the carrier (d Bc) of a real-valued sinusoidal input signal, x. The SNR is determined using a modified periodogram of the same length as the input. The modified periodogram uses a Kaiser window with β = 38. The result excludes the power of the first six harmonics, including the fundamental.exampler = snr ( x, fs, n) returns the SNR in d Bc of a real sinusoidal input signal, x , sampled at a rate fs. The computation excludes the power contained in the lowest n harmonics, including the fundamental. The default value of fs is 1. The default value of n is 6.exampler = snr ( pxx, f ,'psd') specifies the input pxx as a one-sided power spectral density (PSD) estimate. The argument f is a vector of the frequencies at which the estimates of pxx occur. The computation of noise excludes the power of the first six harmonics, including the fundamental.r = snr ( pxx, f, n ,'psd') specifies the number of harmonics, n, to exclude when computing the SNR. The default value of n is 6 and includes the fundamental.exampler = snr ( sxx, f, rbw ,'power') specifies the input as a one-sided power spectrum, sxx , of a real signal. The input rbw is the resolution bandwidth over which each power estimate is integrated.r = snr ( sxx, f, rbw, n ,'power') specifies the number of harmonics, n, to exclude when computing the SNR. The default value of n is 6 and includes the fundamental.exampler = snr ( ___ ,'aliased') removes harmonics of the fundamental that are aliased into the Nyquist range. Use this option when the input signal is undersampled. If you do not specify this option, or if you set it to 'omitaliases' , then the function treats as noise any harmonics of the fundamental frequency that lie beyond the Nyquist range.example [ r, noisepow ] = snr ( ___) also returns the total noise power of the nonharmonic components of the signal.examplesnr ( ___) with no output arguments plots the spectrum of the signal in the current figure window and labels its main features. It uses different colors to draw the fundamental component, the DC value and the harmonics, and the noise. The SNR appears above the plot. This functionality works for all syntaxes listed above except snr (x,y). Examplescollapse all Signal-to-Noise Ratio for Rectangular Pulse with Gaussian Noise Compute the signal-to-noise ratio (SNR) of a 20 ms rectangular pulse sampled for 2 s at 10 k Hz in the presence of Gaussian noise. Set the random number generator to the default settings for reproducible results.rng default Tpulse = 20e-3; Fs = 10e3; t = -1:1/Fs:1; x = rectpuls (t,Tpulse); y = 0.00001*randn (size (x)); s = x + y; pulse SNR = snr (x,s-x)pulse SNR = 80.0818Compare SNR with THD and SINADCompute and compare the signal-to-noise ratio (SNR), the total harmonic distortion (THD), and the signal to noise and distortion ratio (SINAD) of a signal. Create a sinusoidal signal sampled at 48 k Hz. The signal has a fundamental of frequency 1 k Hz and unit amplitude. It additionally contains a 2 k Hz harmonic with half the amplitude and additive noise with variance 0.1².fs = 48e3; t = 0:1/fs:1-1/fs; A = 1.0; powfund = A^2/2; a = 0.4; powharm = a^2/2; s = 0.1; varnoise = s^2; x = A*cos (2*pi*1000*t) + ... a*sin (2*pi*2000*t) + s*randn (size (t));Verify that SNR, THD, and SINAD agree with their definitions. SNR = snr (x); def SNR = 10*log10 (powfund/varnoise); SN = [SNR def SNR]SN = 1×2 17.0178 16.9897THD = thd (x); def THD = 10*log10 (powharm/powfund); TH = [THD def THD]TH = 1×2 -7.9546 -7.9588SINAD = sinad (x); def SINAD = 10*log10 (powfund/ (powharm+varnoise)); SI = [SINAD def SINAD]SI = 1×2 7.4571 7.4473Signal-to-Noise Ratio of Sinusoid Compute the SNR of a 2.5 k Hz sinusoid sampled at 48 k Hz. Add white noise with variance 0.001². Fi = 2500; Fs = 48e3; N = 1024; x = sin (2*pi*Fi/Fs* (1: N)) + 0.001*randn (1,N); SNR = snr (x,Fs)SNR = 57.7103Plot the spectrum and annotate the SNR.snr (x,Fs);SNR of Sinusoid Using PSDObtain the periodogram power spectral density (PSD) estimate of a 2.5 k Hz sinusoid sampled at 48 k Hz. Add white noise with standard deviation 0.00001. Use this value as input to determine the SNR. Set the random number generator to the default settings for reproducible results.rng default Fi = 2500; Fs = 48e3; N = 1024; x = sin (2*pi*Fi/Fs* (1: N)) + 0.00001*randn (1,N); w = kaiser (numel (x),38); [Pxx, F] = periodogram (x,w,numel (x),Fs); SNR = snr (Pxx,F, 'psd')SNR = 97.7446SNR of Sinusoid Using Power Spectrum Using the power spectrum, compute the SNR of a 2.5 k Hz sinusoid sampled at 48 k Hz and embedded in white noise with a standard deviation of 0.00001. Reset the random number generator for reproducible results.rng default Fi = 2500; Fs = 48e3; N = 1024; x = sin (2*pi*Fi/Fs* (1: N)) + 0.00001*randn (1,N); w = kaiser (numel (x),38); [Sxx, F] = periodogram (x,w,numel (x),Fs, 'power' ); rbw = enbw (w,Fs); SNR = snr (Sxx,F,rbw, 'power')SNR = 97.7446Plot the spectrum of the signal and annotate the SNR.snr (Sxx,F,rbw, 'power' );SNR with and Without Aliased Harmonics Generate a signal that resembles the output of a weakly nonlinear amplifier with a 2.1 k Hz tone as input. The signal is sampled for 1 second at 10 k Hz. Compute and plot the power spectrum of the signal. Use a Kaiser window with β = 38 for the computation. Fs = 10000; f = 2100; t = 0:1/Fs:1; x = tanh (sin (2*pi*f*t)+0.1) + 0.001*randn (1,length (t)); periodogram (x,kaiser (length (x),38), [],Fs, 'power')Harmonics stick out from the noise at frequencies of 4.2 k Hz, 6.3 k Hz, 8.4 k Hz, 10.5 k Hz, 12.6 k Hz, and 14.7 k Hz. All frequencies except for the first one are greater than the Nyquist frequency. The harmonics are aliased respectively into 3.7 k Hz, 1.6 k Hz, 0.5 k Hz, 2.6 k Hz, and 4.7 k Hz. Compute the signal-to-noise ratio of the signal. By default, snr treats the aliased harmonics as part of the noise.snr (x,Fs,7);Repeat the computation, but now treat the aliased harmonics as part of the signal.snr (x,Fs,7, 'aliased' );Noise Power Create a sinusoidal signal sampled at 48 k Hz. The signal has a fundamental of frequency 1 k Hz and unit amplitude. It additionally contains a 2 k Hz harmonic with half the amplitude and additive noise with variance 0.1².fs = 48e3; t = 0:1/fs:1-1/fs; A = 1.0; powfund = A^2/2; a = 0.4; powharm = a^2/2; s = 0.1; varnoise = s^2; x = A*cos (2*pi*1000*t) + ... a*sin (2*pi*2000*t) + s*randn (size (t));Compute the noise power in the signal. Verify that it agrees with the definition. [SNR,npow] = snr (x,fs); compare = [10*log10 (powfund)-npow SNR]compare = 1×2 17.0281 17.0178SNR of Amplified Signal Generate a sinusoid of frequency 2.5 k Hz sampled at 50 k Hz. Reset the random number generator. Add Gaussian white noise with standard deviation 0.00005 to the signal. Pass the result through a weakly nonlinear amplifier. Plot the SNR.rng default fs = 5e4; f0 = 2.5e3; N = 1024; t = (0: N-1)/fs; ct = cos (2*pi*f0*t); cd = ct + 0.00005*randn (size (ct)); amp = [1e-5 5e-6 -1e-3 6e-5 1 25e-3]; sgn = polyval (amp,cd); snr (sgn,fs);The DC component and all harmonics, including the fundamental, are excluded from the noise measurement. The fundamental and harmonics are labeled. Input Argumentscollapse allx — Real-valued input signalreal vector Real-valued input signal, specified as a row or column vector. Data Types: double | singley — Noise estimatereal vector Estimate of the noise in the input signal, specified as a real-valued row or column vector. It must have the same dimensions as x. Data Types: double | singlefs — Sample rate1 (default) | positive real scalar Sample rate, specified as a positive scalar. The sample rate is the number of samples per unit time. If the unit of time is seconds, then the sample rate has units of hertz. Data Types: double | singlen — Number of harmonics6 (default) | positive integer scalar Number of harmonics to exclude from the SNR computation, specified as a positive integer scalar. The default value of n is 6.pxx — One-sided PSD estimatevector One-sided power spectral density estimate, specified as a real-valued, nonnegative column vector. The power spectral density must be expressed in linear units, not decibels. Use db2pow to convert decibel values to power values. Example: [pxx,f] = periodogram (cos (pi./ [4;2]* (0:159))'+randn (160,2)) specifies the periodogram PSD estimate of a noisy two-channel sinusoid sampled at 2π Hz and the frequencies at which it is computed. Data Types: double | singlef — Cyclical frequenciesreal-valued row or column vector Cyclical frequencies of the one-sided PSD estimate, pxx , specified as a row or column vector. The first element of f must be 0. Data Types: double | singlesxx — Power spectrumnonnegative real-valued row or column vector Power spectrum, specified as a real-valued nonnegative row or column vector. The power spectrum must be expressed in linear units, not decibels. Use db2pow to convert decibel values to power values. Example: [sxx,w] = periodogram (cos (pi./ [4;2]* (0:159))'+randn (160,2),'power') specifies the periodogram power spectrum estimate of a two-channel sinusoid embedded in white Gaussian noise and the normalized frequencies at which it is computed. Data Types: double | singlerbw — Resolution bandwidthpositive scalar Resolution bandwidth, specified as a positive scalar. The resolution bandwidth is the product of the frequency resolution of the discrete Fourier transform and the equivalent noise bandwidth of the window. Data Types: double | single Output Argumentscollapse allr — Signal-to-noise ratio real-valued scalar Signal-to-noise ratio, expressed in decibels relative to the carrier (d Bc), returned as a real-valued scalar. The SNR is returned in decibels (d B) if the input signal is not sinusoidal. Data Types: double | singlenoisepow — Total noise power real-valued scalar Total noise power of the nonharmonic components of the input signal, returned as a real-valued scalar. Data Types: double | single More Aboutcollapse all Distortion Measurement Functions The functions thd, sfdr, sinad , and snr measure the response of a weakly nonlinear system stimulated by a sinusoid. When given time-domain input, snr performs a periodogram using a Kaiser window with large sidelobe attenuation. To find the fundamental frequency, the algorithm searches the periodogram for the largest nonzero spectral component. It then computes the central moment of all adjacent bins that decrease monotonically away from the maximum. To be detectable, the fundamental should be at least in the second frequency bin. Higher harmonics are at integer multiples of the fundamental frequency. If a harmonic lies within the monotonically decreasing region in the neighborhood of another, its power is considered to belong to the larger harmonic. This larger harmonic may or may not be the fundamental. The function estimates a noise level using the median power in the regions containing only noise. The DC component is excluded from the calculation. The noise at each point is the estimated level or the ordinate of the point, whichever is smaller. The noise is then subtracted from the values of the signal and the harmonics.snr fails if the fundamental is not the highest spectral component in the signal. Ensure that the frequency components are far enough apart to accommodate for the sidelobe width of the Kaiser window. If this is not feasible, you can use the 'power' flag and compute a periodogram with a different window. See Alsosfdr | sinad | thd | toi Topics Analyzing Harmonic Distortion Introduced in R2013b  SNR, RSSI, EIRP and Free Space Path Loss Rajesh Premachandran 09-09-2010 02:51 AMIntroduction Signal to Noise Ratio EIRP (Effective Isotropic Radiated Power)EIRPFree Space Path Loss Free Space Path loss Reference Source Introduction SNR, RSSI, EIRP and Free Space Path Loss Signal to Noise Ratio The power level of the RF signal relative to the power level of the noise floor is known as the Signal-to-Noise ratio or SNR. It is the ratio of signal power to the noise power corrupting the signal. In simple words, SNR (Signal-to-Noise Ratio) is a ratio based value that evaluates your signal based on the noise being seen. SNR is measured as a positive value between 0d B and 120d B and the closer the value is to 120d B, the better. Let's look at the components of the SNR and then understand how SNR is determined. SNR is comprised of 2 values.a) Signalb) Noise RSSI ( Received Signal Strength Indicator) is a more common name for the Signal value. It is the strength that one device is hearing another device. This value is measured in decibels from 0 (zero) to -120 (minus 120). The closer this value to 0 (zero), stronger the signal. Typically voice networks require a -65d Bm or better signal level while a data network needs -80d Bm or better. Normal range in a network would be -45d Bm to -87d Bm depending on power levels and design. The Signal is also affected by the APs transmit power & antenna as well as the client's antenna. Noise is any signal that interferes with your signal. Noise can be due to other wireless devices such as cordless phones, microwave devices etc. This value is measured in decibels from 0 (zero) to -120 (minus 120). Noise level is the amount of interference in your wireless signal, so lower is better. Looking at this value, if the value is closer to -120 (minus 120) it is better because that means there is little to no interference. Typical environments range between -90d Bm and -98d Bm. To calculate the SNR value, we add the Signal Value to the Noise Value and it generates (or should) a positive number that is expressed in decibels (db). For example, lets say your Signal value is -55d Bm and your Noise value is -95d Bm.-55d Bm + -95d Bm = 40db this means you have an SNR of 40, the general rule of thumb is that any SNR above 20 is good. Other important terminologies that we need to understand is the EIRP and Free Space Path Loss. EIRP (Effective Isotropic Radiated Power)EIRP (Effective Isotropic Radiated Power) is the actual amount of signal leaving the antenna and is a value measured in db and is based on 3 values:a) Transmit Power (d Bm) b) Cable Loss (d B) c) Antenna Gain (d Bi)The d B measures the power of a signal as a function of its ratio to another standardized value. The abbreviation d B is often combined with other abbreviations in order to represent the values that are compared. Here are two examples:d Bm—The d B value is compared to 1 m W.d Bw—The d B value is compared to 1 W. You can calculate the power in d Bs from this formula: Power (in d B) = 10 * log10 (Signal/Reference) This list defines the terms in the formula:log10 is logarithm base 10. Signal is the power of the signal (for example, 50 m W). Reference is the reference power (for example, 1 m W). How to find EIRPTo determine EIRP follow this equation:<Transmit Power> - Cable Loss + Antenna Gain = EIRPFor example we have a Cisco 1242AG access points running at full power with a 6d Bi antenna on the 802.11a radio and a 2.5d Bi antenna on the 802.11bg radio.802.11a EIRP = 17d Bm (40mw) - 0d B + 6d Bi = 23d Bm = 200mw of actual output power802.11bg EIRP = 20d Bm (100mw) - 0d B + 2.5d Bi = 22.5d Bm = 150mw (approx) of actual output power Based on the example above, in theory, if you were to measure it right at the antenna you could get an RSSI of -23d Bm or -22.5d Bm respectively. Free Space Path Loss Free space path loss is a weakening of the RF signal due to a broadening of the wave front. It is a measure of how much signal power the device loses over a given distance. Typically the device loses about 0.020 d B per foot in an outdoor or wide open office; doors, walls, glass, and etc. affect this. This is why as a client walks away from an AP, the signal gets weaker. All this relates to the client because it determines the signal the client receives, also keep in mind that when looking at the client you have to account for it's antenna as well much like the EIRP. So if a client card has a 2 d Bi antenna (although they are typically either 0d Bi or 2.2d Bi) that boosts the incoming signal, and assuming the actual RSSI signal being seen is -68d Bm, then: Actual RSSI + Antenna Gain = Displayed RSSI-68d Bm + 2d Bm = -66d Bm Check out the Cisco Enterprise Mobility Design Guide for more detail information on WLAN Radio Frequency Design Considerations. Free Space Path lossfree space path loss is a major issue when dealing with RF links at a long distance, particularly outdoors. Cisco has a couple of good calculator tools to allow for free space path loss in the RF link budget design calculations. To explain free space path loss use the following formula. FSPL = ( 4 π d / λ ) 2= ( 4 π d f / c ) 2Where: FSPL is the Free space path lossd is the distance of the receiver from the transmitter (metres)λ is the signal wavelength (metres)f is the signal frequency (Hertz)c is the speed of light in a vacuum (metres per second)This is actually part of the MESH RF boot camp class that was required to get your Outdoor MESH ATP. If you fail to consider free space path loss on an outdoor MESH network the MESH links will surely fail. Reference WLAN Radio Frequency Design Considerations Wireless, LAN (WLAN) - RF Power Values Sourcehttps://supportforums.cisco.com/message/3145716https://supportforums.cisco.com/thread/2039792Tags: access access-point aironet antenna apconfiguration effective_isotropic_radiated_power eirpeirp_and_free_space_path_loss free_space_path_loss rssisignal_to_noise_ratio snr troubleshoot wirelesswireless_access_point  Blood test codes and results explained This section helps you to understand what blood tests your doctor has ordered, why they have been ordered, and what the results may mean. It is only a guide, if any of your blood test results are abnormal you should consult with your doctor. This is an excellent website that gives a thorough explanation all blood tests. It is easy to use and allows you to select your country of origin... http://labtestsonline.org.au/ *NRR = Normal Reference Range. Please note that the figures quoted can vary between pathology labs. When you receive a copy of your results, NRR for that lab will be displayed next to each result. Contents1 Antibody Titer2 FBC or CBC3 E. S. R.4 C. R. P.5 LFT6 U and E7 Haematology- differential8 Ferritin9 B12 and folate10 TPMT11 Prometheus IBD sgi Diagnostic Antibody Titer Antibody Titer tests are performed to determine your Immune Response to an Antigen. This may be a Immunization or Vacine, Microbe (i.e. Virus, Bacteria, or Fungus), Chemical, Allergen or Substances produced by your body ("Self" Proteins). The most common method of Antibody Titer testing is done by ELISA. Antibody Titers can be performed on multiple different body fluids depending on what your doctor is testing and can include: - Blood / Serum Test - Urine / Urinalysis - Saliva (Spit) - Mucus FBC or CBCFBC (Full Blood Count) or CBC (Complete Blood Count). This measures the red and white blood cells, and platelets in the blood. It is standard whenever blood is tested. Haemoglobin / Hemoglobin (U. S) NRR 13.2-16.2 gm/d L (Male) 12.0-15.2 gm/d L (Female) - used in the red blood cells to carry oxygen around the body. Low haemoglobin indicates anaemia, which can have several causes. Platelets NRR 140-450x103/µL - helps the blood to clot. Too low indicates you are at risk of excessive bleeding, and is called Thrombocytopenia. A platelet count that is too high is called Thrombocythemia and can cause Clubbed Fingers and increased risk of Blood Clots. WBC NRR 4.1-10.9x103/µL - White blood count. Too low indicates the immune system is suppressed. Too high can indicate infection. MCH NRR 26-34 pg - Mean corpsicle haemoglobin. The average amount of haemoglobin in each red blood cell. Too low can indicate iron deficiency anaemia. MCHC NRR 31-35 gm/d L - Mean corpsicle haemoglobin concentration. Whether the red blood cell has the right amount of haemoglobin for its size. In cases of iron deficiency anaemia, this result may be normal. HCT NRR 40-52% (Male) 37-46% (Female) 31-43% (Child) - Haematocrit. Measures the percentage of red blood cells in whole blood. It is an indicator of anaemia, bleeding and nutritional deficiencies (B12, Iron and Folate). MCV NRR 82-102 f L (Male) 78-101 f L (Female) - Mean corpsicle volume. Whether the red blood cells are the right size. Too low can indicate iron deficiency anaemia. RBC NRR 4.3-6.2x106/µL (Male) 3.8-5.5x106/µL (Female) 3.8-5.5x106/µL (Infant/Child) - Red blood count. The number of red blood cells in the blood. This result may be normal in iron deficiency anaemia. E. S. R. Erythrocyte sedimentation rate. NRR male <50 years 1-7 mm/hour >50 years 2-10 mm/hour, female <50 years 3-9 mm/hour >50 years 5-15 mm/hour. How 'sticky' the proteins in the blood are. Too high indicates acute inflammation in the body. ESR changes quite quickly, therefore can be used to assess the effectiveness of medications. However ESR can be raised by other inflammation in the body (non-IBD related). C. R. P. C-Reactive Protein. NRR <5.0 mg/L. Too high indicates chronic (ongoing) inflammation in the body. CRP can be used to assess remission/flare status. Note: some patients can have low CRP even in a flare. For more information on CRP Click HERELFTLiver function tests. Assesses how well the liver is functioning. Used to monitor patients taking azathioprine, to ensure the medication is not damaging the liver. ALT NRR 5-40 U/L - Alanine Transaminase is an enzyme that is released into the blood when the liver is damaged or diseased. Gamma GT NRR males <50 U/L, females <30 U/L - Gamma-glutamyl transpeptidase, detects diseases of the liver and bile ducts. Total Bilirubin NRR 2-20 mol/L - this is a product formed from destroying old red blood cells. Total Alk. Phos. NRR adult, non pregnant 25-100 U/L, growing children 70-300 U/L - Alkaline Phosphatase, helps to detect liver disease. Albumin NRR 35-47 g/L - helps to detect disorders affecting the liver and kidney. Low levels can also be an indicator malnutrition, malabsorption and severe inflammation. U and EUrea and electrolytes. Used to assess kidney function. Sodium NRR 135-145 mmol/L - this is one of the electrolytes used within cells. It is processed from salt. Too high or low can mean kidneys are not functioning properly, that the person is suffering from dehydration, they are not absorbing salt correctly (particularly in patients with terminal ileum involvement) or the diet is too high or low in salt. Potassium NRR 3.8-4.9 mmol/L - this is another electrolyte used within cells. Too high or low can indicate problems with kidney function, dehydration or diet. Urea NRR 3.0-8.0 mmol/L - This is a waste product within the blood, that the kidneys filter out to form urine. Too high can indicate a problem with the kidneys or dehydration. Creatinine NRR 0.05-0.12 mmol/L - Is a waste chemical that is filtered by the kidney. High levels may indicate damage to the kidney. Haematology- differential This measures the different types of white blood cells. Numbers given are absolutes (that is the actual number of each type present rather than as a proportion of all the white blood cells). If the overall WBC is too high or low, the numbers of each type of white blood cell can help the physician to determine the cause. Neutrophils NRR 2.0-7.5 x 109/L - high levels may indicate acute infection, stress or Rheumatoid Arthritis. Low levels may be due to widespread bacterial infection, influenza or caused as side effect of some of the drugs used to treat IBD Lymphocytes NRR 1.5-4.0 x 109/L - raised levels may be due to chronic infection, viral infection or infectious hepatitis. Low levels may be caused by sepsis or from the side effects of some of the drugs used to treat IBD. Monocytes NRR 0.2-0.8 x 109/L - These can be raised through stress, inflammation, or immune disorders. They can be low after treatment with glucocorticosteroids (such as prednisolone ). Eosinophils NRR 0.04-0.4 x 109/L - If these are too high it may indicate the presence of an eosinophilic disorder, which can have similar symptoms to an IBD. Basophils NRR <0.1 x 109/L - levels increase when there is inflammation present caused by things like an allergic reaction or Asthma. Ferritin Iron stores. NRR male 30-300 µg/L, female 15-200 µg/L. The body needs iron to make haemoglobin. Low ferritin indicates iron deficiency, however ferritin levels can be artificially raised if inflammation is present. B12 and folate B12 NRR 120-680 pmol/L, Folate NRR serum 7-45 nmol/L. These are two b-vitamins, that your body needs for the processing of energy. Too low usually indicates a problem with absorption, however vegans may lnot get enough b12 in their diet and should consider supplements. TPMTThiopurine s-methyltransferase. NRR >17.0 U/m L RBC (normal) 11.9-17.0 U/m L RBC (ambiguous range) 15.4-17.0 U/m L RBC (probable low normal) 11.9-15.3 U/m L RBC (possible carrier) 6.0-11.8 U/m L RBC (carrier range) 0.0-5.9 U/m L RBC (homozygous deficient range) TPMT is usually ordered by the doctor if you are about to start treatment with a thiopurine drug such as Azathioprine. If you have no detectable TPMT activity then you are at risk of developing severe side effects to thiopurine drugs. Usually the doctor will find an alternative drug treatment. A low blood TPMT activity puts you at risk of less serious side effects such as hair loss, stomach pain, diarrhoea and inflammation of your pancreas. In this case the doctor may reduce the dose of thiopurine drug given. Prometheus IBD sgi Diagnostic The Prometheus IBD sgi Diagnostic is used to diagnose Inflammatory Bowel Disease and differentiate between Crohn's Disease and Ulcerative Colitis. For more information please see the Prometheus IBD sgi Diagnostic HERE. Popular T hreads Discussing Blood test codes and results explained CRP level 164Got A Copy Of My BW Results  What is a MERV, MPR, or FPR Rating for AC and Furnace Filters? What is a MERV, MPR, or FPR Rating for AC and Furnace Filters? MERV Rating is the accepted M inimum E fficiency R eporting V alue for air conditioner furnace filter media as determined by the American Society of Heating, Refrigerating, and Air Conditioning Engineers, (ASHRAE) . MERV is the primary international air conditioner furnace filter industry standard and is used for rating the ability of a furnace filter to capture and hold particles and pollutants. The measurement used in these ratings is a Micrometer, or micron. A micron is one millionth of a meter (0.000001m) and is not visible to the human eye. A piece of copy paper is about 100 microns thick. A human hair averages 80 microns in diameter. Pet dander is 2-4 microns in size and can linger in the air for hours before it settles on a surface!Best Filters.com uses the MERV Rating system. We have all standard sizes of AC & Furnace Air Filters available in MERV 8, 10 and 12 ratings. These pleated, 100% synthetic media filters maintain an electrostatic charge to attract and capture fine particulates. In the average American home, the most common air filter is a MERV 4. These are usually the fiberglass furnace filters that you can see through and do not stop particles smaller than 10 microns. These MERV 4 filters will only protect your equipment and will not help with allergens or even larger particles. We do not recommend MERV 4 filters and do not carry them. We do carry MERV 8, 10 and 12 rated pleated filters. Most residential systems are well able to use replacement filters up to MERV 12. MERV Rating is the established air filter industry rating system, but, some companies have developed their own rating systems, based on the ASHRAE MERV Rating. MPR Rating, or Microparticle Performance Rating, was developed by a large manufacturer (3M) to grade their air filters based on the ability to filter air particles smaller than 1 micron. The microparticle performance rating is not considered to be the industry standard by the American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE). The published MPR Rating numbering system is a scale of 0 2700, with their highest published furnace filter equaling a MERV 13. FPR Rating, or air Filter Performance Rating, is a grading system that uses a color/number system on a scale of 4 (green circle) to 10 (blue circle). Some of their air conditioner filter descriptions refer to the MERV Rating and the MPR Rating, but don't always agree. Its important to note that the MERV Rating is the MINIMUM initial efficiency rating. Its the efficiency rating given to an air conditioner furnace filter when it is brand new, as the new air conditioner furnace filter traps more debris, it actually and somewhat surprisingly, becomes more efficient at trapping particles as time goes by. Eventually, though, every air filter will trap the very tiny particles until it becomes so dirty that air cannot get through and if the filter is not replaced prior to this point, significant damage may occur to your HVAC or furnace. MERV, MPR, FPR, RATINGMERV Rating MPR Rating FPR Rating ASHRAE MINIMUM INITIAL EFFICIENCY Containment and Particles Uses0.30 to 1.0 Microns 1.0 to 3.0 Microns 3.0 - 10.0 Microns MERV 19-20 (HEPA) N/A N/A 99.99-99.999% < 0.30 Micron carbon dust sea salt all combustion smoke Clean Room Manufacturing Electronics Manufacturing Pharmaceuticals Carcinogenic Materials Hospital Inpatient Care Surgery Superior Commercial Buildings MERV 17-18 (HEPA) N/A N/A > 95%MERV 16 (HEPA) N/A N/A > 95% > 95% > 95%MERV 14-15 N/A N/A 75 - 95% > 90% > 90% .30 to 1.0 Microns All Bacteria Tobacco Smoke Fireplace Smoke Droplet w/Virus (sneeze) Smog MERV 13 N/A 10 Blue Rating < 75% > 90% > 90% Superior Residential Property Superior Commercial Property MERV 12 Blue 1900 (BEST)80 - 90% > 90%8-9 Purple Rating 1.0 to 3.0 Microns Auto Emissions Dust Baking Flour Pet Dander MERV 11 7 Red Rating 65 - 79% > 85%MERV 10 Red 1000 (BETTER)50 - 64% > 85% Residential Commercial Industrial Workspaces MERV 8 White 600 (GOOD) 5 Green Rating 70 - 85% 3.0 to 10.00 Mold Spores Household Dust/Spray Hair Spray Dust Mite Pollen Sanding Dust Textile / Carpet Fibers MERV 7 50 - 69% Minimum filtration workspace Window units Fiberglass filters polyester air filters MERV 6 400 35 - 49%MERV 0 - MERV 5 20 - 34  Signal-to-noise ratio From Wikipedia, the free encyclopedianavigation search For "signal-to-noise ratio" in statistics, see Effect size. For other uses, see Signal to Noise (disambiguation). Part of a series on Antennas Common types [show]Components [show]Systems [show]Safety and regulation [show]Radiation sources / regions [show]Characteristics [hide]Array gain Directivity Efficiency Electrical length Equivalent radius Factor Friis transmission equation Gain Height Radiation pattern Radiation resistance Radio propagation Radio spectrum Signal-to-noise ratio Spurious emission Techniques [show]v t e Signal-to-noise ratio (abbreviated SNR or S/N) is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. SNR is defined as the ratio of signal power to the noise power, often expressed in decibels. A ratio higher than 1:1 (greater than 0 d B) indicates more signal than noise. While SNR is commonly quoted for electrical signals, it can be applied to any form of signal for example isotope levels in an ice core or biochemical signaling between cells or financial trading signals. The signal-to-noise ratio, the bandwidth, and the channel capacity of a communication channel are connected by the Shannon–Hartley theorem. Signal-to-noise ratio is sometimes used metaphorically to refer to the ratio of useful information to false or irrelevant data in a conversation or exchange. For example, in online discussion forums and other online communities, off-topic posts and spam are regarded as "noise" that interferes with the "signal" of appropriate discussion. [1]Contents [ hide ]1 Definition1.1 Decibels1.2 Dynamic range1.3 Difference from conventional power2 Alternative definition3 SNR for various modulation systems3.1 Amplitude modulation3.2 Frequency modulation4 Improving SNR in practice5 Digital signals5.1 Fixed point5.2 Floating point6 Optical SNR7 Types and abbreviations8 See also9 Notes10 References11 External links Definition [ edit]Signal-to-noise ratio is defined as the ratio of the power of a signal (meaningful information) and the power of background noise (unwanted signal):where P is average power. Both signal and noise power must be measured at the same or equivalent points in a system, and within the same system bandwidth. If the variance of the signal and noise are known, and the signal and noise are both zero-mean, SNR can be: [2]If the signal and the noise are measured across the same impedance, the SNR can be obtained by calculating the square of the amplitude ratio: ()where A is root mean square (RMS) amplitude (for example, RMS voltage). Decibels [ edit]Because many signals have a very wide dynamic range, signals are often expressed using the logarithmic decibel scale. Based upon the definition of decibel, signal and noise may be expressed in decibels (d B) asand In a similar manner, SNR may be expressed in decibels as Using the definition of SNR ()Using the quotient rule for logarithms ()Substituting the definitions of SNR, signal, and noise in decibels into the above equation results in an important formula for calculating the signal to noise ratio in decibels, when the signal and noise are also in decibels: In the above formula, P is measured in units of power, such as Watts or mili Watts, and signal-to-noise ratio is a pure number. However, when the signal and noise are measured in Volts or Amperes, which are measures of amplitudes, they must be squared to be proportional to power as shown below: [ ()] ()Dynamic range [ edit]The concepts of signal-to-noise ratio and dynamic range are closely related. Dynamic range measures the ratio between the strongest un- distorted signal on a channel and the minimum discernible signal, which for most purposes is the noise level. SNR measures the ratio between an arbitrary signal level (not necessarily the most powerful signal possible) and noise. Measuring signal-to-noise ratios requires the selection of a representative or reference signal. In audio engineering, the reference signal is usually a sine wave at a standardized nominal or alignment level, such as 1 k Hz at +4 d Bu (1.228 V RMS ). SNR is usually taken to indicate an average signal-to-noise ratio, as it is possible that (near) instantaneous signal-to-noise ratios will be considerably different. The concept can be understood as normalizing the noise level to 1 (0 d B) and measuring how far the signal 'stands out'. [note 1]Difference from conventional power [ edit]In physics, the average power of an AC signal is defined as the average value of voltage times current; for resistive (non- reactive) circuits, where voltage and current are in phase, this is equivalent to the product of the rms voltage and current: But in signal processing and communication, one usually assumes that [ citation needed] so that factor is usually not included while measuring power or energy of a signal. This may cause some clarity among readers, but the resistance factor is not significant for typical operations performed in signal processing, or for computing power ratios. For most cases, the power of a signal would be considered to be simplywhere 'A' is the amplitude [ clarification needed] of the AC signal. Alternative definition [ edit]An alternative definition of SNR is as the reciprocal of the coefficient of variation, i.e., the ratio of mean to standard deviation of a signal or measurement: [4] [5]where is the signal mean or expected value and is the standard deviation of the noise, or an estimate thereof. [note 2] Notice that such an alternative definition is only useful for variables that are always non-negative (such as photon counts and luminance ). Thus it is commonly used in image processing, [6] [7] [8] [9] where the SNR of an image is usually calculated as the ratio of the mean pixel value to the standard deviation of the pixel values over a given neighborhood. Sometimes SNR is defined as the square of the alternative definition above. The Rose criterion (named after Albert Rose) states that an SNR of at least 5 is needed to be able to distinguish image features at 100% certainty. An SNR less than 5 means less than 100% certainty in identifying image details. [5] [10]Yet another alternative, very specific and distinct definition of SNR is employed to characterize sensitivity of imaging systems; see Signal-to-noise ratio (imaging). Related measures are the " contrast ratio " and the " contrast-to-noise ratio ". SNR for various modulation systems [ edit]Amplitude modulation [ edit]Channel signal-to-noise ratio is given bywhere W is the bandwidth and is modulation index Output signal-to-noise ratio (of AM receiver) is given by Frequency modulation [ edit]Channel signal-to-noise ratio is given by Output signal-to-noise ratio is given by Improving SNR in practice [ edit]Recording of the noise of a thermogravimetric analysis device that is poorly isolated from a mechanical point of view; the middle of the curve shows a lower noise, due to a lesser surrounding human activity at night. All real measurements are disturbed by noise. This includes electronic noise, but can also include external events that affect the measured phenomenon — wind, vibrations, gravitational attraction of the moon, variations of temperature, variations of humidity, etc., depending on what is measured and of the sensitivity of the device. It is often possible to reduce the noise by controlling the environment. Otherwise, when the characteristics of the noise are known and are different from the signals, it is possible to filter it or to process the signal. For example, it is sometimes possible to use a lock-in amplifier to modulate and confine the signal within a very narrow bandwidth and then filter the detected signal to the narrow band where it resides, thereby eliminating most of the broadband noise. When the signal is constant or periodic and the noise is random, it is possible to enhance the SNR by averaging the measurement. In this case the noise goes down as the square root of the number of averaged samples. Additionally, internal noise of electronic systems can be reduced by low-noise amplifiers. Digital signals [ edit]When a measurement is digitized, the number of bits used to represent the measurement determines the maximum possible signal-to-noise ratio. This is because the minimum possible noise level is the error caused by the quantization of the signal, sometimes called Quantization noise. This noise level is non-linear and signal-dependent; different calculations exist for different signal models. Quantization noise is modeled as an analog error signal summed with the signal before quantization ("additive noise"). This theoretical maximum SNR assumes a perfect input signal. If the input signal is already noisy (as is usually the case), the signal's noise may be larger than the quantization noise. Real analog-to-digital converters also have other sources of noise that further decrease the SNR compared to the theoretical maximum from the idealized quantization noise, including the intentional addition of dither. Although noise levels in a digital system can be expressed using SNR, it is more common to use E b/N o, the energy per bit per noise power spectral density. The modulation error ratio (MER) is a measure of the SNR in a digitally modulated signal. Fixed point [ edit]See also: Fixed point arithmetic For n -bit integers with equal distance between quantization levels ( uniform quantization) the dynamic range (DR) is also determined. Assuming a uniform distribution of input signal values, the quantization noise is a uniformly distributed random signal with a peak-to-peak amplitude of one quantization level, making the amplitude ratio 2 n /1. The formula is then: This relationship is the origin of statements like " 16-bit audio has a dynamic range of 96 d B". Each extra quantization bit increases the dynamic range by roughly 6 d B. Assuming a full-scale sine wave signal (that is, the quantizer is designed such that it has the same minimum and maximum values as the input signal), the quantization noise approximates a sawtooth wave with peak-to-peak amplitude of one quantization level [11] and uniform distribution. In this case, the SNR is approximately Floating point [ edit]Floating-point numbers provide a way to trade off signal-to-noise ratio for an increase in dynamic range. For n bit floating-point numbers, with n-m bits in the mantissa and m bits in the exponent: Note that the dynamic range is much larger than fixed-point, but at a cost of a worse signal-to-noise ratio. This makes floating-point preferable in situations where the dynamic range is large or unpredictable. Fixed-point's simpler implementations can be used with no signal quality disadvantage in systems where dynamic range is less than 6.02m. The very large dynamic range of floating-point can be a disadvantage, since it requires more forethought in designing algorithms. [12] [note 3] [note 4]Optical SNR [ edit]Optical signals have a carrier frequency that is much higher than the modulation frequency (about 200 THz and more). This way the noise covers a bandwidth that is much wider than the signal itself. The resulting signal influence relies mainly on the filtering of the noise. To describe the signal quality without taking the receiver into account, the optical SNR (OSNR) is used. The OSNR is the ratio between the signal power and the noise power in a given bandwidth. Most commonly a reference bandwidth of 0.1 nm is used. This bandwidth is independent of the modulation format, the frequency and the receiver. For instance an OSNR of 20 d B/0.1 nm could be given, even the signal of 40 GBit DPSK would not fit in this bandwidth. OSNR is measured with an optical spectrum analyzer. Types and abbreviations [ edit]Signal to noise ratio may be abbreviated as SNR and less commonly as S/N. PSNR stands for Peak signal-to-noise ratio. GSNR stands for Geometric Signal-to-Noise Ratio. SINR is the Signal-to-noise-plus-interference ratio. See also [ edit]Audio system measurements Generation loss Matched filter Near-far problem Noise margin Omega ratio Peak signal-to-noise ratio Signal-to-noise statistic Signal-to-noise-plus-interference ratio Signal to noise ratio (imaging)SINADSubjective video quality Total harmonic distortion Video quality Notes [ edit]^ The connection between optical power and voltage in an imaging system is linear. This usually means that the SNR of the electrical signal is calculated by the 10 log rule. With an interferometric system, however, where interest lies in the signal from one arm only, the field of the electromagnetic wave is proportional to the voltage (assuming that the intensity in the second, the reference arm is constant). Therefore the optical power of the measurement arm is directly proportional to the electrical power and electrical signals from optical interferometry are following the 20 log rule. [3]^ The exact methods may vary between fields. For example, if the signal data are known to be constant, then can be calculated using the standard deviation of the signal. If the signal data are not constant, then can be calculated from data where the signal is zero or relatively constant.^ Often special filters are used to weight the noise: DIN-A, DIN-B, DIN-C, DIN-D, CCIR-601; for video, special filters such as comb filters may be used.^ Maximum possible full scale signal can be charged as peak-to-peak or as RMS. Audio uses RMS, Video P-P, which gave +9 d B more SNR for video. References [ edit]^ Breeding, Andy (2004). The Music Internet Untangled: Using Online Services to Expand Your Musical Horizons. Giant Path. p. 128. ISBN 9781932340020.^ "Signal-to-noise ratio". scholarpedia.org.^ Michael A. Choma, Marinko V. Sarunic, Changhuei Yang, Joseph A. Izatt. Sensitivity advantage of swept source and Fourier domain optical coherence tomography. Optics Express, 11 (18). Sept 2003.^ D. J. Schroeder (1999). Astronomical optics (2nd ed.). Academic Press. p. 433. ISBN 978-0-12-629810-9.^ a b Bushberg, J. T., et al., The Essential Physics of Medical Imaging, (2e). Philadelphia: Lippincott Williams & Wilkins, 2006, p. 280.^ Rafael C. González, Richard Eugene Woods (2008). Digital image processing. Prentice Hall. p. 354. ISBN 0-13-168728-X.^ Tania Stathaki (2008). Image fusion: algorithms and applications. Academic Press. p. 471. ISBN 0-12-372529-1.^ Jitendra R. Raol (2009). Multi-Sensor Data Fusion: Theory and Practice. CRC Press. ISBN 1-4398-0003-0.^ John C. Russ (2007). The image processing handbook. CRC Press. ISBN 0-8493-7254-2.^ Rose, Albert (1973). Vision – Human and Electronic. Plenum Press. p. 10. ISBN 9780306307324. [...] to reduce the number of false alarms to below unity, we will need [...] a signal whose amplitude is 4–5 times larger than the rms noise.^ Defining and Testing Dynamic Parameters in High-Speed ADCs — Maxim Integrated Products Application note 728^ Fixed-Point vs. Floating-Point DSP for Superior Audio — Rane Corporation technical library External links [ edit]Taking the Mystery out of the Infamous Formula,"SNR = 6.02N + 1.76d B," and Why You Should Care. [1] Analog Devices ADC and DAC Glossary – Maxim Integrated Products Understand SINAD, ENOB, SNR, THD, THD + N, and SFDR so you don't get lost in the noise floor – Analog Devices The Relationship of dynamic range to data word size in digital audio processing Calculation of signal-to-noise ratio, noise voltage, and noise level Learning by simulations – a simulation showing the improvement of the SNR by time averaging Dynamic Performance Testing of Digital Audio D/A Converters Fundamental theorem of analog circuits: a minimum level of power must be dissipated to maintain a level of SNRInteractive webdemo of visualization of SNR in a QAM constellation diagram Institute of Telecommunicatons, University of Stuttgart [ hide]v t e Noise (physics and telecommunications)General Acoustic quieting Distortion Noise cancellation Noise control Noise measurement Noise power Noise reduction Noise temperature Phase distortion Noise in... Audio Buildings Electronics Environment Government regulation Human health Images Radio Rooms Ships Sound masking Transportation Video Class of noise Additive white Gaussian noise (AWGN) Atmospheric noise Background noise Brownian noise Burst noise Cosmic noise Flicker noise Gaussian noise Grey noise Jitter Johnson–Nyquist noise (thermal noise) Pink noise Quantization error (or q. noise) Shot noise White noise Coherent noise Value noise Gradient noise Worley noise Engineering terms Channel noise level Circuit noise level Effective input noise temperature Equivalent noise resistance Equivalent pulse code modulation noise Impulse noise (audio) Noise figure Noise floor Noise shaping Noise spectral density Noise, vibration, and harshness (NVH) Phase noise Pseudorandom noise Statistical noise Ratios Carrier-to-noise ratio ( C / N) Carrier-to-receiver noise density ( C / k T) d Brn C E b/N 0 (energy per bit to noise density)E s/N 0 (energy per symbol to noise density) Modulation error ratio ( MER) Signal, noise and distortion ( SINAD)Signal-to-interference ratio ( S / I) Signal-to-noise ratio ( S / N , SNR) Signal-to-noise ratio (imaging)Signal to noise plus interference ( SNIR) Signal-to-quantization-noise ratio ( SQNR) Contrast-to-noise ratio ( CNR)Related topics List of noise topics Acoustics Colors of noise Interference (communication) Noise generator Radio noise source Spectrum analyzer Thermal radiation Categories: Engineering ratios Error measures Measurement Electrical parameters Audio amplifier specifications Noise (electronics) Statistical ratios  . What is Noise Dosimeter? Noise Dosimeter can be used to measure noise pollution in personal areas, workplaces, and recreational places. It is also known as personal sound exposure meter (PSEM) and follows International Standard IEC 61252. Noise Dosimeter typically measures four parameters:● Dose - Dose is expressed as percentage. If environment is more noisy, Dose percentage is higher. Threshold of safety is 100%.● Time Weighted Average (TWA) - TWA is average sound level in decibel (d B). If environment is more noisy, TWA is higher.● Projected Dose (p Dose) - p Dose is 8-hour projected dose based on actual Dose measurement over actual run time.● Projected Time Weighted Average (p TWA) - p TWA is 8-hour projected sound level based on actual TWA over actual run time. Based on Noise Dosimeter, selection of hearing protection can be determined. In order to monitor noise safety, user needs to see Health Text Message at the bottom of Sound Meter+. Also, if a display item is flashing, it means current environment is dangerous for hearing.  What Does RMS Stand for in Speakers? When you read the specifications for audio speakers, you'll likely come across the term RMS, which stands for "Root Mean Square," a method for rating a speaker's ability to handle audio signal power. Although it is technical in nature, you don't need to understand the details completely to use RMS specifications effectively to compare different audio speakers. Video of the Day Close-up of an audio speakercredit: Kelly ISP/i Stock/Getty Images Average, Peak and RMSAudio engineers measure power in terms of average, peak and RMS watts. Peak power is simply the highest reading obtained when measuring the playback of a typical song; it is the most power a speaker can handle in a loud burst of sound. By contrast, average power tells you what a speaker can manage for sustained periods. Mathematically, it is the alternating current voltage across a speaker's terminals times the current through the speaker, multiplied by the power factor, a number related to the speaker's efficiency. RMS power is the speaker current divided by 1.414, the square root of two. This gives a number somewhat smaller than the average and reflects a more accurate sustained power capability for a speaker. Comparing Speakers Because the peak power figure is the highest of the three ratings, speaker manufacturers may use it in advertising to make a speaker "look good." Average and RMS ratings, however, are lower numbers that give you a better idea of a speaker's capabilities. Always compare the RMS rating of one model against the RMS for another; never compare RMS versus peak, as they mean different things.  Noise and Hearing Protection Noise and Hearing Protection Patient Health Information One in 10 Americans has a hearing loss that affects his or her ability to understand normal speech. Age-related hearing loss is the most common cause of this condition and is more prevalent than hearing loss caused by excessive noise exposure. However, exposure to excessive noise can damage hearing, and it is important to understand the effects of this kind of noise, particularly because such exposure is avoidable. What causes hearing loss? The ear has three main parts: the outer, middle, and inner ear. The outer ear (the part you can see) opens into the ear canal. The eardrum separates the ear canal from the middle ear. Small bones in the middle ear help transfer sound vibrations to the inner ear. Here, the vibrations become nerve impulses, which the brain interprets as music, a slamming door, a voice, and so on. When noise is too loud, it begins to kill the nerve endings in the inner ear. Prolonged exposure to loud noise destroys nerve endings. As the number of nerve endings decreases, so does your hearing. There is no way to restore life to dead nerve endings; the damage is permanent. The longer you are exposed to a loud noise, the more damaging it may be. Also, the closer you are to the source of intense noise, the more damaging it is. How can I tell if a noise is dangerous? People differ in their sensitivity to noise. As a general rule, noise may damage your hearing if you are at arms length and have to shout to make yourself heard. If noise is hurting your ears, your ears may ring, or you may have difficulty hearing for several hours after exposure to the noise. Noise is characterized by intensity, measured in decibels; pitch, measured in hertz or kilohertz; and duration. Can noise affect more than my hearing? A ringing in the ears, called tinnitus, commonly occurs after noise exposure, and often becomes permanent. Some people react to loud noise with anxiety and irritability, an increase in pulse rate and blood pressure, or an increase in stomach acid. Very loud noise can reduce efficiency in performing difficult tasks by diverting attention from the job. How can I protect myself against noise? Wear hearing protectors, especially if you must work in an excessively noisy environment. You should also wear them when using power tools, noisy yard equipment, or firearms, or riding a motorcycle or snowmobile. Hearing protectors come in two forms: earplugs and earmuffs. Earplugs are small inserts that fit into the outer ear canal. They must be sealed snugly so the entire circumference of the ear canal is blocked. An improperly fitted, dirty, or worn-out plug may not seal properly and can result in irritation of the ear canal. Plugs are available in a variety of shapes and sizes to fit individual ear canals and can be custom-made. For people who have trouble keeping them in their ears, the plugs can be fitted to a headband. Earmuffs fit over the entire outer ear to form an air seal so the entire circumference of the ear canal is blocked, and they are held in place by an adjustable band. Earmuffs will not seal around eyeglasses or long hair, and the adjustable headband tension must be sufficient to hold earmuffs firmly in place. Earplugs and earmuffs can be found at most pharmacies. Will I hear other people and machine problems if I wear hearing protectors? Just as sunglasses help vision in very bright light, so hearing protectors enhance speech understanding in very noisy places. Even in a quiet setting, a normal-hearing person wearing hearing protectors should be able to understand a regular conversation. Hearing protectors do slightly reduce the ability of those with damaged hearing or poor comprehension of language to understand normal conversation. However, it is essential that persons with impaired hearing wear earplugs or muffs to prevent further inner ear damage in very noisy places. It has been argued that hearing protectors might reduce a workers ability to hear the noises that signify an improperly functioning machine. However, most workers readily adjust to the quieter sounds and can still detect such problems. If a worker is already hearing impaired, he or she needs expert advice about how to protect against further damage. In some cases hearing aids can and should be used under earmuffs. How can I tell if my hearing is damaged? Hearing loss usually develops over a period of several years. Because it is painless and gradual, you might not notice it. What you might notice is a ringing or other sound in your ear (tinnitus), which could be the result of long-term exposure to noise that has damaged hearing nerves. Or you may have trouble understanding what people say; they may seem to be mumbling, especially when you are in a noisy place such as a crowd or a party. This could be the beginning of high-frequency hearing loss; a hearing test will detect it. If you have any of these symptoms, they may be caused by impacted wax or an ear infection, which are relatively easy to correct. However, you may suffer from noise-related hearing loss. In any case, take no chances with noisethe hearing loss it causes is permanent. If you suspect hearing loss, consult a physician with special training in ear care and hearing disorders (called an otolaryngologist or otologist). This doctor can diagnose your hearing problem and recommend the best way to manage it. For more information on the laws for on-the-job noise exposure, please refer to the information provided at www.entnet.org. Sound Measurements Decibels (d B) measure the intensity of sound. The scale runs from the faintest sound the human ear can detect, which is labeled 0 d B, to more than 180 d B, the noise at a rocket pad during launch. Most experts agree that continual exposure to more than 85 decibels is dangerous. Recent studies show an alarming increase in noise-related hearing loss in young people. Approximate examples of decibel levels: Faintest sound heard by human ear: 0 d BWhisper, quiet library: 30 d BNormal conversation, sewing machine, typewriter: 60 d BLawnmower, shop tools, truck traffic: 90 d BChainsaw, pneumatic drill, snowmobile: 100 d BSandblasting, loud rock concert, auto horn: 115 d BGun muzzle blast, jet engine (such noise can cause pain and even brief exposure injures unprotected ears): 149 d BThe Occupational Safety and Health Administrations limit for noise without hearing protectors: 140 d BPitch is the frequency of sound vibrations per second measured in hertz or kilohertz, and duration. A low pitch, such as a deep voice or a tuba, makes fewer vibrations per second than a high voice or violinthe higher the pitch, the higher the frequency. Loss of high-frequency hearing also can make speech sound muffled. Patient Health Home Copyright © 2018 American Academy of Otolaryngology–Head and Neck Surgery. Reproduction or republication strictly prohibited without prior written permission. More Resources About: Otology/Neurotology Ears Related Links Better Ear Health Hearing Loss Noise-Induced Hearing Loss in Children Noise-Induced Hearing Loss: Q&A  CCIE or Null! Just some more details on how drastically different wireless networks differ from the traditional wired network is understanding the client connection. Surely we all understand how the wired connection works, we plug in a cable two of the four pairs carry data then speed and duplex setting are auto-negotatiated. However when you look at a wireless client you see an antenna, signal strength, data rate, RSSI, power level, and SNR values definitely a little more to think about. I’ll start with RSSI, which is the Received Signal Strength Indicator this value is typically shown as a negative d Bm value (d B and watt values are a topic for another post). RSSI is the measurement of power in an RF signal, the more power in an RF signal the better the connection quality is. So the closer this value is to 0 the stronger the signal is. So a value of -61 is stronger then a value of -74. Now different vendors do have different scales some vendors will have a max value of -100 while others go higher or lower, of course signals that weak should be avoided (and probably won’t work anyway). So it’s best to get some documentation from the vendor of your client WLAN cards to see the RSSI value range. The value of the RSSI will also play a role in the connection speed, and once again vendor documentation will provide the RSSI value to link speed ratio (and do keep in mind many other factors play a role in the connection speed as well). SNR is the Signal to Noise ratio, this is how much stronger the wireless signal is compared to the noise floor surrounding the WLAN client. This is shown in a positive d B value. Too much RF noise around the WLAN client will cause collisions resulting in frames being retransmitted thus lowering the throughput of the connection. Try connecting a cordless phone that works in the 2.4 GHz range right next to a b/g access point, the phone can generate enough RF noise to cancel out the wireless signal completely. It’s typically best practice to have the SNR value 20 to 25 d B’s away from the RSSI value. So to go back to our previous example if our RSSI is -61 we would want our SNR value to be around -86, or if our RSSI is -74 we would want the SNR to be -99. The data rate can be one of many values depending on which wireless standard you are connecting with. Be aware though that wireless is a shared medium so it’s half duplex it can not transmit and receive at the same time. So your actual throughput will be about half of what your client is connecting at. A WLAN device showing a connection of 54 Mbps will really have throughput of maybe 30 Mbps. Throughput can be tested using nice little utility called iperf which is available on both Windows and Linux platforms for free. The power level is measured in m W and depicts how much power a WLAN device is using to maintain the connection. Its typically best practice to design your WLAN infrastructure so your devices operate at half their max output power. This way if an AP goes down neighboring AP’s can double their output power and maintain the availability of the WLAN. So the overall signal strength/quality registered by client will be a mixture of all those variables. Below is a screen shot from the Cisco Aironet Site Survey Utility Here you will see the RSSI at -50 d Bm and noise level of -96 d Bm, resulting in an SNR value of 46 d B. This utility will also provide you with the BSSID (MAC Address) of the AP you are connecting to along with the RF Channel, 64 in this case utilizing 802.11a. Share this: Linked In Print Facebook Twitter Google Email Loading... Related Control roaming behavior on your Cisco wireless network. In "Cisco Wireless"Cisco band select and client RSSI. In "Cisco Wireless"But I've got an 'Excellent Signal'!!? In "Wireless"  . You should wear a hearing protection device whenever you are exposed to noise that is 85 decibels or greater for an 8-hour period of time.  . RSRP (Reference Signal Recieved Power)RSRP is the linear average of reference singal power (in Watts) accorss the specified bandwidth (in number of REs). This is the most important item UE has to measure for cell selection, reselection and handover. You can think of this as the one similar to CPICH RSCP in WCDMA. The formal definition of RSRP in 3GPP 36.214 is as follows : Reference signal received power (RSRP), is defined as the linear average over the power contributions (in [W]) of the resource elements that carry cell-specific reference signalswithin the considered measurement frequency bandwidth. For RSRP determination the cell-specific reference signals R0 according TS 36.211 shall be used. If the UE can reliably detect that R1 is available it may use R1 in addition to R0 to determine RSRP. Note : R0 is the Cell Specific Reference Signal for Antenna Port 0 and R1 is the Cell Specific Reference signal for Antenna Port 1 (Refer to 36.211 Figure 6.10.1.2-1. Mapping of downlink reference signals (normal cyclic prefix))Following is an example of one downlink radio frame. The red part is the resource elements in which reference signal is being transmitted. RSRP is the linear average of all the red part power. Since this measures only the reference power, we can say this is the strength of the wanted signal. But it does not gives any information about signal quality. RSRP gives us the signal strenth of the desired signal, not the quality of the signal. For quality of the signal information another parameter called 'RSSQ' is used in some case. UE usually measures RSRP or RSRQ based on the direction (RRC message) from the network and report the value. When it report this value, it does use the real RSRP value. It sends a non-negative value ranging from 0 to 97 and each of these values are mapped to a specific range of real RSRP value as shown in the following table from 36.133. For practical calculation example, refer to RSRQ Calculator (You Tube)Just to relieve a little of headache to figure out the mapping between the reported RSRP and measured value in d Bm, I just made precalculated table as shown below. RSRPFrom To Unit00-140d Bm01-140-139d Bm02-139-138d Bm03-138-137d Bm04-137-136d Bm05-136-135d Bm06-135-134d Bm07-134-133d Bm08-133-132d Bm09-132-131d Bm10-131-130d Bm11-130-129d Bm12-129-128d Bm13-128-127d Bm14-127-126d Bm15-126-125d Bm16-125-124d Bm17-124-123d Bm18-123-122d Bm19-122-121d Bm20-121-120d Bm21-120-119d Bm22-119-118d Bm23-118-117d Bm24-117-116d Bm25-116-115d Bm26-115-114d Bm27-114-113d Bm28-113-112d Bm29-112-111d Bm30-111-110d Bm31-110-109d Bm32-109-108d Bm33-108-107d Bm34-107-106d Bm35-106-105d Bm36-105-104d Bm37-104-103d Bm38-103-102d Bm39-102-101d Bm40-101-100d Bm41-100-99d Bm42-99-98d Bm43-98-97d Bm44-97-96d Bm45-96-95d Bm46-95-94d Bm47-94-93d Bm48-93-92d Bm49-92-91d Bm50-91-90d Bm51-90-89d Bm52-89-88d Bm53-88-87d Bm54-87-86d Bm55-86-85d Bm56-85-84d Bm57-84-83d Bm58-83-82d Bm59-82-81d Bm60-81-80d Bm61-80-79d Bm62-79-78d Bm63-78-77d Bm64-77-76d Bm65-76-75d Bm66-75-74d Bm67-74-73d Bm68-73-72d Bm69-72-71d Bm70-71-70d Bm71-70-69d Bm72-69-68d Bm73-68-67d Bm74-67-66d Bm75-66-65d Bm76-65-64d Bm77-64-63d Bm78-63-62d Bm79-62-61d Bm80-61-60d Bm81-60-59d Bm82-59-58d Bm83-58-57d Bm84-57-56d Bm85-56-55d Bm86-55-54d Bm87-54-53d Bm88-53-52d Bm89-52-51d Bm90-51-50d Bm91-50-49d Bm92-49-48d Bm93-48-47d Bm94-47-46d Bm95-46-45d Bm96-45-44d Bm97-44d Bm Reference : [1] 3GPP - 36.214 Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer - Measurements [2] 3GPP - 36.133 Evolved Universal Terrestrial Radio Access (E-UTRA);Requirements for support of radio resource management [3] For practical calculation example, refer to RSRQ Calculator (You Tube) [4] RSRP and RSRQ Measurement in LTE  Water and Dust Resistant Rating - IP Scale Water and Dust Resistant Rating - IP Scale Water and Dust Resistant Rating - IP Scale IP Ratings Defined When is "Rugged" tough enough? You may hear about IP ratings from computer equipment manufactures or systems integrators. For example, what does an IP rating of IP34 really mean? Will that be enough for your facility? if you are using a barcode scanner in an office environment, IP34 will probably work for you, but if you bring that same unit into a warehouse or a light industrial environment, that equipment probably won’t last through one shift. Before investing in a hardware device, make sure it can satisfy the requirements of your facility. While a IP67 rating won’t protect your unit from being run over by a forklift, it will guarantee reliable performance in a dusty warehouse environment or in an outdoor environment with all types of weather conditions. When Rugged is Rugged enough for your environment? The more rugged a device the higher in cost it is going to be, so in order to stay within budget you will want to make sure you don't buy too much ruggedness for what your environment calls for. What is an IP rating? IP stands for Ingress Protection. This IP rating is used to specify the strength of the enclosure that surrounds electronic equipment and is determined by specific tests. Each IP rating consists of using two separate measures. The first is protection against solids; the second number is protection against liquids. Rating = Protection from Solids Protection from Liquids IP00 = No protection No protection IP01 = No protection condensation IP02 = No protection water spray < 15 degrees from vertical IP03 = No protection water spray < 60 degrees from vertical IP04 = No protection water spray from any direction IP05 = No protection low pressure water jets from any direction IP06 = No protection high pressure water jets from any direction IP07 = No protection immersion between 15cm and 1m depth IP08 = No protection long term immersion to a specified pressure IP10 = touch by hands (>50mm) No protection IP11 = touch by hands (>50mm) condensation IP12 = touch by hands (>50mm) water spray < 15 degrees from vertical IP13 = touch by hands (>50mm) water spray < 60 degrees from vertical IP14 = touch by hands (>50mm) water spray from any direction IP15 = touch by hands (>50mm) low pressure water jets from any direction IP16 = touch by hands (>50mm) high pressure water jets from any direction IP17 = touch by hands (>50mm) immersion between 15cm and 1m depth IP18 = touch by hands (>50mm) long term immersion to a specified pressure IP20 = touch by fingers (>12mm) No protection IP21 = touch by fingers (>12mm) condensation IP22 = touch by fingers (>12mm) water spray < 15 degrees from vertical IP23 = touch by fingers (>12mm) water spray < 60 degrees from vertical IP24 = touch by fingers (>12mm) water spray from any direction IP25 = touch by fingers (>12mm) low pressure water jets from any direction IP26 = touch by fingers (>12mm) high pressure water jets from any direction IP27 = touch by fingers (>12mm) immersion between 15cm and 1m depth IP28 = touch by fingers (>12mm) long term immersion to a specified pressure IP30 = tools & wires (>2.5mm) No protection IP31 = tools & wires (>2.5mm) condensation IP32 = tools & wires (>2.5mm) water spray < 15 degrees from vertical IP33 = tools & wires (>2.5mm) water spray < 60 degrees from vertical IP34 = tools & wires (>2.5mm) water spray from any direction IP35 = tools & wires (>2.5mm) low pressure water jets from any direction IP36 = tools & wires (>2.5mm) high pressure water jets from any direction IP37 = tools & wires (>2.5mm) immersion between 15cm and 1m depth IP38 = tools & wires (>2.5mm) long term immersion to a specified pressure IP40 = tools & small wires (>1mm) No protection IP41 = tools & small wires (>1mm) condensation IP42 = tools & small wires (>1mm) water spray < 15 degrees from vertical IP43 = tools & small wires (>1mm) water spray < 60 degrees from vertical IP44 = tools & small wires (>1mm) water spray from any direction IP45 = tools & small wires (>1mm) low pressure water jets from any direction IP46 = tools & small wires (>1mm) high pressure water jets from any direction IP47 = tools & small wires (>1mm) immersion between 15cm and 1m depth IP48 = tools & small wires (>1mm) long term immersion to a specified pressure IP50 = Limited dust ingress protection No protection IP51 = Limited dust ingress protection condensation IP52 = Limited dust ingress protection water spray < 15 degrees from vertical IP53 = Limited dust ingress protection water spray < 60 degrees from vertical IP54 = Limited dust ingress protection water spray from any direction IP55 = Limited dust ingress protection low pressure water jets from any direction IP56 = Limited dust ingress protection high pressure water jets from any direction IP57 = Limited dust ingress protection immersion between 15cm and 1m depth IP58 = Limited dust ingress protection long term immersion to a specified pressure IP60 = Total dust ingress protection No protection IP61 = Total dust ingress protection condensation IP62 = Total dust ingress protection water spray < 15 degrees from vertical IP63 = Total dust ingress protection water spray < 60 degrees from vertical IP64 = Total dust ingress protection water spray from any direction IP65 = Total dust ingress protection low pressure water jets from any direction IP66 = Total dust ingress protection high pressure water jets from any direction IP67 = Total dust ingress protection immersion between 15cm and 1m depth IP68 = Total dust ingress protection long term immersion to a specified pressure IP69K = Total dust ingress protection steam jet cleaning  Noise Reduction Rating (NRR) Noise Reduction Rating (NRR)Definition - What does Noise Reduction Rating (NRR) mean? Noise Reduction Rating (NRR) is the difference between the overall C-weighted sound level of a noise spectrum having equal energy per octave and the resulting A-weighted noise levels under a hearing protection device. Free Webinar | Hazardous Materials: Is Your Chemical Storage Solution Compliant? | May 10 @ 1 PM (ET)Safeopedia explains Noise Reduction Rating (NRR)Noise Reduction Rating is used to evaluate and determine the effictiveness or fit of noise protection equipment for a given work environment. NRR is specifically the measurement, in decibles, of how well hearing protection reduces noise as specified by the Environmental Protection Agency. The higher the NRR number the greater the noise reduction. While wearing hearing protection your exposure to noise is equal to the total noise level minus the NRR of the hearing protectors in use. For example, if you were exposed to 80db of noise but were wearing earplugs with an NRR of 29, your actual noise exposure would only be 51d B.  Non-return-to-zero The binary signal is encoded using rectangular pulse-amplitude modulation with polar NRZ (L), or polar non-return-to-zero-level code In telecommunication, a non-return-to-zero ( NRZ) line code is a binary code in which ones are represented by one significant condition, usually a positive voltage, while zeros are represented by some other significant condition, usually a negative voltage, with no other neutral or rest condition. The pulses in NRZ have more energy than a return-to-zero (RZ) code, which also has an additional rest state beside the conditions for ones and zeros. NRZ is not inherently a self-clocking signal, so some additional synchronization technique must be used for avoiding bit slips; examples of such techniques are a run-length-limited constraint and a parallel synchronization signal. For a given data signaling rate, i.e., bit rate, the NRZ code requires only half the baseband bandwidth required by the Manchester code (the passband bandwidth is the same). When used to represent data in an asynchronous communication scheme, the absence of a neutral state requires other mechanisms for bit synchronization when a separate clock signal is not available. NRZ-level itself is not a synchronous system but rather an encoding that can be used in either a synchronous or asynchronous transmission environment, that is, with or without an explicit clock signal involved. Because of this, it is not strictly necessary to discuss how the NRZ-level encoding acts "on a clock edge" or "during a clock cycle", since all transitions happen in the given amount of time representing the actual or implied integral clock cycle. The real question is that of sampling—the high or low state will be received correctly provided the transmission line has stabilized for that bit when the physical line level is sampled at the receiving end. However, it is helpful to see NRZ transitions as happening on the trailing (falling) clock edge in order to compare NRZ-level to other encoding methods, such as the mentioned Manchester code, which requires clock edge information (is the XOR of the clock and NRZ, actually) see the difference between NRZ-mark and NRZ-inverted. Contents [ hide ]1 Variants1.1 Unipolar non-return-to-zero level1.2 Bipolar non-return-to-zero level1.3 Non-return-to-zero space1.4 Non-return-to-zero inverted1.5 Randomized non-return-to-zero2 See also3 References4 Further reading Variants [ edit]NRZ can refer to any of the following serializer line codes: Code name Alternate name Complete name Description NRZ (L)NRZL Non-return-to-zero level Appears as raw binary bits without any coding. Typically binary 1 maps to logic-level high, and binary 0 maps to logic-level low. Inverse logic mapping is also a type of NRZ (L) code. NRZ (I)NRZI Non-return-to-zero inverted Refers to either an NRZ (M) or NRZ (S) code. NRZ (M)NRZM Non-return-to-zero mark Serializer mapping {0: constant, 1: toggle}. NRZ (S)NRZS Non-return-to-zero space Serializer mapping {0: toggle, 1: constant}. NRZ (C)NRZC Non-return-to-zero change The NRZ code also can be classified as a polar or non-polar, where polar refers to a mapping to voltages of +V and −V, and non-polar refers to a voltage mapping of +V and 0, for the corresponding binary values of 0 and 1. Unipolar non-return-to-zero level [ edit]Main article: Unipolar encoding Unipolar NRZ (L), or unipolar non-return-to-zero level"One" is represented by a DC bias on the transmission line (conventionally positive), while "zero" is represented by the absence of bias – the line at 0 volts or grounded. For this reason it is also known as "on-off keying". In clock language, a "one" transitions to or remains at a biased level on the trailing clock edge of the previous bit, while "zero" transitions to or remains at no bias on the trailing clock edge of the previous bit. Among the disadvantages of unipolar NRZ is that it allows for long series without change, which makes synchronization difficult, although this is not unique to the unipolar case. One solution is to not send bytes without transitions. More critically, and unique to unipolar NRZ, are issues related to the presence of a transmitted DC level – the power spectrum of the transmitted signal does not approach zero at zero frequency. This leads to two significant problems: first, the transmitted DC power leads to higher power losses than other encodings, and second, the presence of a DC signal component requires that the transmission line be DC-coupled. Bipolar non-return-to-zero level [ edit]"One" is represented by one physical level (usually a positive voltage), while "zero" is represented by another level (usually a negative voltage). In clock language, in bipolar NRZ-level the voltage "swings" from positive to negative on the trailing edge of the previous bit clock cycle. An example of this is RS-232, where "one" is −12 V to −5 V and "zero" is +5 V to +12 V. Non-return-to-zero space [ edit]Non-return-to-zero space Encoder for NRZS, toggle on zero"One" is represented by no change in physical level, while "zero" is represented by a change in physical level. In clock language, the level transitions on the trailing clock edge of the previous bit to represent a "zero". This "change-on-zero" is used by High-Level Data Link Control and USB. They both avoid long periods of no transitions (even when the data contains long sequences of 1 bits) by using zero-bit insertion. HDLC transmitters insert a 0 bit after 5 contiguous 1 bits (except when transmitting the frame delimiter "01111110"). USB transmitters insert a 0 bit after 6 consecutive 1 bits. The receiver at the far end uses every transition — both from 0 bits in the data and these extra non-data 0 bits — to maintain clock synchronization. The receiver otherwise ignores these non-data 0 bits. Non-return-to-zero inverted [ edit]An example of the NRZI encoding, transition on 1The opposite convention, transition on 0Encoder for NRZI, toggle on one Non-return-to-zero, inverted ( NRZI, also known as Nonreturn to Zero IBM [1], Inhibit code [2] or IBM code [2]) was devised by Bryon E. Phelps ( IBM) in 1956. [2] [3] It is a method of mapping a binary signal to a physical signal for transmission over some transmission media. The two-level NRZI signal distinguishes data bits by the presence or absence of a transition at a clock boundary. Which bit value corresponds to a transition varies in practice, and the name NRZI is used for both. Run-length limited (RLL) codes are generally described using the convention that a logical 1 is transmitted as a transition, and a logical 0 is transmitted as no transition. The HDLC and Universal Serial Bus protocols use the opposite convention: a logical 0 is transmitted as a transition, and a logical 1 is transmitted as no transition. A long series of no-transition bits can be difficult for a receiver to count accurately, so some means for forcing a transition at reasonable intervals is generally used in addition to NRZI. Magnetic disk and tape storage devices generally use fixed-rate RLL codes, while HDLC and USB use bit stuffing: they insert an additional 0 bit (forcing a transition) after 5 or 6 (respectively) consecutive 1 bits. While bit stuffing is efficient, it results in a variable data rate because it takes slightly longer to send a long string of 1 bits than it does to send a long string of 0 bits. Synchronized NRZI ( NRZI-S, SNRZI) and group-coded recording (GCR) are modified forms of NRZI. [4] In NRZI-S, each 8-bit group is extended to 9 bits by a 1 in order to establish a transition for synchronisation. [4]Randomized non-return-to-zero [ edit]This section needs expansion. You can help by adding to it. (June 2017) [5]See also [ edit]Wikimedia Commons has media related to Non return to zero. Bipolar encoding Enhanced non-return-to-zero-Level E-NRZ-LReturn-to-zero Line code Universal asynchronous receiver/transmitter Manchester code References [ edit]^ IBM 729 II, IV, V, VI Magnetic Tape Units (PDF) (223-6988 ed.). 1962. p. 7. Retrieved 12 February 2018.^ a b c Palmer, Dean (2005). "Section 1: Recording Systems, 1: A brief history of magnetic recording". In Vasic, Bane; Kurtas, Erozan M. Coding and Signal Processing for Magnetic Recording Systems (1st ed.). CRC Press LLC. pp. I–6, I–15. ISBN 0-8493-1524-7.^ US 2774646, Phelps, Bryon E., "Magnetic recording method", published 1956-12-18, assigned to IBM [1] (See also: DE950858C)^ a b Patel, Arvind Motibhai (1988). "5. Signal and Error-Control Coding". In Mee, C. Denis; Daniel, Eric D. Magnetic Recording. II: Computer Data Storage (1st ed.). Mc Graw-Hill Book Company. ISBN 0-07-041272-3.^ Watkinson, John (1990). "3.7. Randomized NRZ". Coding for Digital Recording. Stoneham, MA, USA: Focal Press. pp. 64–65. ISBN 0-240-51293-6. ISBN 978-0-240-51293-8. Further reading [ edit]Brey, Barry. The Intel Microprocessors. Columbus: Pearson Prentice Hall. ISBN 0-13-119506-9. This article incorporates public domain material from the General Services Administration document "Federal Standard 1037C" (in support of MIL-STD-188 ). [ hide]v t e Line coding (digital baseband transmission)Main articles Unipolar encoding Bipolar encoding On-off keying Basic line codes Return to zero (RZ) Non-return-to-zero, level (NRZ/NRZ-L)Non-return-to-zero, inverted (NRZ-I)Non-return-to-zero, space (NRZ-S) Manchester Differential Manchester/biphase (Bi-φ)Extended line codes Conditioned Diphase 4B3T 4B5B 2B1Q Alternate mark inversion Modified AMI code Coded mark inversion MLT-3 encoding Hybrid ternary code 6b/8b encoding 8b/10b encoding64b/66b encoding Eight-to-fourteen modulation Delay/Miller encoding TC-PAMOptical line codes Carrier-suppressed return-to-zero Alternate-phase return-to-zero See also: Baseband Baud Bit rate Digital signal Digital transmission Ethernet physical layer Pulse modulation methods Pulse-amplitude modulation (PAM) Pulse code modulation (PCM) Serial communication Category: Line codes  Explaining Sound Ratings Explaining Sound Ratings The four types of sound ratings referenced on this site are STC, OITC, IIC, and Delta IIC (ΔIIC). Below is a summary of each of these ratings and how they might relate to your project. STCSTC stands for sound transmission class. This is the most common rating used in North America for determining airborne sound transmission loss between 125 and 4,000 Hz. This range covers the majority of common noises we hear including speech, television, music, dogs barking, and other similar annoyances. A higher STC rating often shows improved performance. However, the rating is essentially an average over the 16 frequency points tested. Because of this, a product can perform exceptionally well in one range, poorly in another, and still end up with a better STC rating than a competing product that may have performed better in a frequency range more relevant to your project requirements. This is a pretty common occurrence that should not be ignored when comparing products. Sort through the misleading ratings by gaining access to actual sound test data showing the STC contour line on the transmission loss graph. The performance in relation to the STC contour line will reveal the consistency of the product over the most common frequencies. The STC rating for a basic insulated 2×4 wall with a single layer of drywall on each side is 35-38. This rating increases to STC 42-45 with steel studs. The STC rating for a basic wood structure floor/ceiling is 40-43. The STC rating for a six inch concrete sub-floor is 52-55. A good level of isolation for walls and ceilings is STC 50 plus. A high level of isolation for walls is STC 60 plus with ceilings at STC 50 plus. Products like Genie Clips® RST, Green Glue Compound in tubes or pails, and Total Mass MLV Barrier are most commonly used to improve STC ratings. OITCOITC stands for outside inside transmission class. The original purpose of the OITC rating was to determine performance of products in relation to exterior noise, which is often heavy in low frequencies. We also use the OITC rating to determine a product’s value for use in low frequency sensitive areas such as home theaters and recording studios. The OITC rating represents transmission loss results from 80 to 4,000 Hz using a different mathematical equation than the STC rating. The results express in decibels as opposed to the point system used to determine STC ratings and with weighting more towards low frequency performance. A higher number shows better performance. Extreme mass and decoupling are requirements to isolate low frequencies. As a result, OITC ratings are typically much lower than STC ratings. When planning an isolation project, the OITC rating is often more crucial than the STC rating. This is because of the inclusion of the 80 and 100 Hz frequencies in the OITC calculation. These two frequencies are now more commonplace thanks to high quality speakers and sub-woofers. Products like Genie Clips® RST, Green Glue Compound in tubes or pails are most commonly used to improve OITC ratings. IICIIC stands for impact insulation class. Acoustic labs conduct the IIC test using a tapping machine with steel faced hammers. These hammers strike a test floor material generating sounds between 125 to 4,000 Hz. The impact creates vibrations that travel through the floor into the receiving side (the room below). The engineer plots the results of each tap on a graph, compares the results to the reference assembly, and determines the IIC rating from comparing these two tests. A higher number shows better performance. The IIC rating does not account for any squeaking or rattling caused by loose wood frame construction. Nor does it account for low frequency footfall noise or structural deflection. The IIC ratings for basic concrete sub-floor with no resilient underlayment is around 28 to 35 IIC. The IIC ratings for basic wood structure with no resilient underlayment is around 40 to 45 IIC. Without the addition of sound isolation products, the IIC rating of basic wood structures will rate better than concrete structures because they are naturally more resilient. An IIC rating of 50 and above is most common in building code and HOA requirements. The Genie Clips® RST are most commonly used on the ceiling to improve the IIC rating, while Genie Mat® RST rubber underlayment is most commonly used on the floor to improve the IIC rating.. Delta IIC (ΔIIC)The Delta IIC rating shows what the product adds to the assembly in terms of isolating impact footfall noise. The Delta IIC test starts by testing a full assembly, typically six to eight inches of concrete, with nothing above or below the concrete. Then an underlayment installs directly to the concrete, and the same test repeats. The Delta IIC rating is the performance gain between the first and second test. A higher number shows better performance. The Delta IIC rating is the best rating to consider when comparing the performance of different types of underlayment. It keeps the manufacturers from promoting misleading results obtained by using materials or methods of isolation that the average assembly does not use. Misleading results are most often found with claims of 60 IIC or above using materials less than 1/2” thick. They achieve their astronomical rating with decoupled ceilings and considerable additional mass, but will claim their thin underlayment is what achieved that IIC rating. If the IIC rating is unreasonably high, then ask to see a Delta IIC rating. If they cannot provide a Delta IIC rating, then ignore the advertised ratings.  . Sound level is usually defined in terms of something called Sound Pressure Level (SPL). SPL is actually a ratio of the absolute, Sound Pressure and a reference level (usually the Threshold of Hearing, or the lowest intensity sound that can be heard by most people). SPL is measured in decibels (d B), because of the incredibly broad range of intensities we can hear. SPL can be measured with a Sound Pressure Level Meter, available from some consumer electronics stores for fairly reasonable prices. It's a lot more complicated than that, so if you're technically inclined and want to learn more about sound, check out the incredibly detailed "Handbook for Acoustic Ecology" . Less technically adventurous people might want to browse around the lastest Google hits for "Sound Pressure Level" .  Thread: What does SNR / AGC / BER mean? 21-11-12, 00:05 #1garyblas Senior Member Join Date Apr 2012Posts 996Thanks 70Thanked 81 Times in 63 Posts What does SNR / AGC / BER mean? I think SNR is the signal to noise ratio What is AGC and BER ? If i check my channels my free to air SNR is 95% but on Sky channels im only getting 68%.. Im guessing my dish needs tweeking in? But the AGC on both is over 90 whilst the BER is zero? Vu+ Duo --- Vix Apollo --- Magic HD Night Skin Sponsored by World-of-Satellite.co.uk21-11-12, 00:12 #2Larry-GV. I. PJoin Date May 2010Posts 32,545Thanks 7,821Thanked 22,869 Times in 12,371 Posts SNR = Signal to Noise Ratio - which means signal quality AGC = Automatic Gain Control - which means signal strength BER = Bit Error Rate - which shows the error rate of the signal. So, SNR and AGC should be as high as possible. BER should be as low as possible, like 0. It can be higher, if your other values are higher. My posts contain my own personal thoughts and opinions, they do not represent those of any organisation or group but my own. If you don't like what I post, Don't read it. SIMPLES. The Following 4 Users Say Thank You to Larry-G For This Useful Post:aadham (06-12-17), garyblas (21-11-12), judge (21-11-12), keysimm (17-07-17)21-11-12, 00:19 #3garyblas Senior Member Join Date Apr 2012Posts 996Thanks 70Thanked 81 Times in 63 Posts Originally Posted by pheonix SNR = Signal to Noise Ratio - which means signal quality AGC = Automatic Gain Control - which means signal strength BER = Bit Error Rate - which shows the error rate of the signal. So, SNR and AGC should be as high as possible. BER should be as low as possible, like 0. It can be higher, if your other values are higher. Thanks Phoenix for info. So in my case my BER is zero - which is perfect, my AGC is over 90% which is good but my SNR on Sky channels is only 68%. I do get some freezes , not many. Would you suggest tweeking the dish? Im only using Sky mini dish Vu+ Duo --- Vix Apollo --- Magic HD Night Skin21-11-12, 00:23 #4Larry-GV. I. PJoin Date May 2010Posts 32,545Thanks 7,821Thanked 22,869 Times in 12,371 Postsmaybe see if the LNB needs to be skewed before you go fiddling with the dish. My posts contain my own personal thoughts and opinions, they do not represent those of any organisation or group but my own. If you don't like what I post, Don't read it. SIMPLES.21-11-12, 00:26 #5garyblas Senior Member Join Date Apr 2012Posts 996Thanks 70Thanked 81 Times in 63 Posts Originally Posted by pheonixmaybe see if the LNB needs to be skewed before you go fiddling with the dish. So try twisting the LNB and see if it improves ? Vu+ Duo --- Vix Apollo --- Magic HD Night Skin21-11-12, 00:31 #6Larry-GV. I. PJoin Date May 2010Posts 32,545Thanks 7,821Thanked 22,869 Times in 12,371 Posts Originally Posted by garyblas So try twisting the LNB and see if it improves ? basically yes, there will be a set of numbers on the side the the lnb where it meets the collar and a arrow or similar on the collar it self. have a look at this map for a general idea of the skew settings for your area. My posts contain my own personal thoughts and opinions, they do not represent those of any organisation or group but my own. If you don't like what I post, Don't read it. SIMPLES. The Following 2 Users Say Thank You to Larry-G For This Useful Post: Double Tap (27-03-13), garyblas (21-11-12)21-11-12, 00:36 #7garyblas Senior Member Join Date Apr 2012Posts 996Thanks 70Thanked 81 Times in 63 Posts Cheers mate will give it a go, I assume it is set to area 3 as getting 68 % but will try a little tweek. Thanks again Vu+ Duo --- Vix Apollo --- Magic HD Night Skin21-11-12, 00:42 #8Larry-GV. I. PJoin Date May 2010Posts 32,545Thanks 7,821Thanked 22,869 Times in 12,371 Posts To be brutally honest i really would not worry too much as long as your channels work fine, I fine that my SNR has to drop below 60% before i start to notice a problem on some channels, even then most are still on unless it gets below 50%. My posts contain my own personal thoughts and opinions, they do not represent those of any organisation or group but my own. If you don't like what I post, Don't read it. SIMPLES.21-11-12, 00:49 #9garyblas Senior Member Join Date Apr 2012Posts 996Thanks 70Thanked 81 Times in 63 Posts I dont loose the channel and picture is fine generally, but i do find ITV4 HD freezes more.. this is typically a SNR of 58% I will have a look at LNB setting, can aways mark its position and tweek back if all goes wrong or worse. Thanks for your help as usual. Vu+ Duo --- Vix Apollo --- Magic HD Night Skin27-03-13, 15:20 #10Double Tap Junior Member Join Date Mar 2012Location UKPosts 10Thanks 5Thanked 0 Times in 0 Posts Originally Posted by pheonixbasically yes, there will be a set of numbers on the side the the lnb where it meets the collar and a arrow or similar on the collar it self. have a look at this map for a general idea of the skew settings for your area. what about when you have a movable dish setup does it auto skew for the other satellite positions can you go into any settings to alter your skew settings as I used to have a uniden Rx plus separate uniden positioner granted it did have a pair of wires going to the polarizer but then again the ram had a hole bunch of conductors going to it. Now all replaced with just a single coax & digital electrickery.  . Top definition ANR/ABFANR/ABF stands for: A Nursing Relationship /Adult Breast Feeding. ANR/ABF refers to a relationship involving sucking milk from the female breast as an expression of close intimacy. Adult Nursing Relationships depend on a stable and long term relationship of the couple, otherwise it is nearly impossible to maintain a steady milk flow. On the other hand it is frequently reported that breastfeeding has a strong stabilizing effect on the partnership. The breastfeeding woman may experience orgasms or a pleasurable let-down reflex. Examples of usage of the term ANR /ABF: I could totally go ANR on that tig-bitty bitch ! alt: I could totally go ABF on that tig-bitty bitch!#sucking #breasts #boobs #nursing #adult #relationship #breastfeedingby Foqqman January 17, 2007592 229The Urban Dictionary Mug One side has the word, one side has the definition. Microwave and dishwasher safe. Lotsa space for your liquids. Buy the mug  What is an STC Rating? STC Ratings What is an STC Rating? STC stands for Sound Transmission Class. Basically, STC ratings are an established way to average how much sound is stopped by something. STC ratings are used for windows, doors, walls and most building materials. For windows, STC ratings range from 18 to 38. STC ratings are the ONLY way to accurately compare various noise reduction products. An STC rating is an instrument measurement of how much noise is stopped. The STC ratings allow accurate ‘apple to apple’ comparisons. The STC rating is the average amount of noise stopped at 18 different frequencies, measured in decibels. STC ratings are a logarithmic scale similar to the earthquake Richter Scale, which means each number is significantly higher than the one before. What STC Ratings do Windows Have? For single pane windows, the STC Rating is most likely between 26 and 28. The difference is the glass thickness and how air-tight the window is. Louvered windows can be less than STC rating 18 in many cases. STC Rating Values, Noise Reduction The table below shows typical window STC rating values for single pane windows and dual pane windows, and the resulting STC rating when Soundproof Windows are installed over both single pane windows and dual pane windows. Window Glass Normal STC Range Typical Value Single pane glass 26-28 27Dual pane glass 26-32 26Soundproof Window over a single pane window 48-54 48Soundproof Window over a dual pane window 48-54 48The STC Ratings for double paned windows usually vary from 26 to 33. Most have good air seals, but the variation is due to the glass thickness and the amount of air space between the glass. The bigger air space and thicker glass is preferred. Soundproof Windows range from 48 to 54 (with more possible), which varies depending on the existing window and the air space. Over a single-paned window in a standard wall, the STC rating is 48. Over double paned windows, the STC rating is 48 or more. With increases of air space, figures greater than 50 are easily achieved. Why the STC Rating Numbers are so Close in Value STC rating measurement uses a special scale like the Richter Scale for earthquakes. An increase from 28 to 38 means 90% of the noise is reduced. A change from 28 to 43 represents a noise reduction of over 95%. Small increases can mean a lot of extra noise reduction. The increase from 38 to 43 mentioned above does not sound like much (90% versus 95+% in reductions) – but going from 90% to over 95% means that 60% of the remaining noise was removed; every number represents a large amount of noise. Use of STC for Noise Reduction Comparisons Using STC ratings bases noise on measurable facts, not opinions. The higher the STC, the more sound is stopped; each point is significant and important. Dual Pane Windows will not Stop Noise When good, thick dual pane windows rated at STC 35 are installed (replaced existing single pane windows with STC 27), the sound will not be reduced much. Often, until the STC rating is up in the 40’s, the noise is not reduced enough to stop it from being a significant problem. The human ear becomes more sensitive to sound as the volume reduces, so in many cases, more significant noise reductions are necessary to resolve the problem.100% Noise Reduction? While Soundproof Windows cannot eliminate 100% of the noise, they will reduce the noise very significantly. In many cases less noise will be coming through the Soundproof Windows than the walls. Most walls have an STC of 43-48: Soundproof Windows usually have an STC rating of 48-54. Several things can be done to increase the window STC values even more. Contact us for a free evaluation of your situation today!  Gross rating point From Wikipedia, the free encyclopedianavigation search This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (December 2015) ( Learn how and when to remove this template message)In advertising, a gross rating point ( GRP) is a measure of the size of an advertising campaign by a specific medium or schedule. It does not measure the size of the audience reached. Rather, GRPs quantify impressions as a percentage of the target population, and this percentage may thus be greater than, or in fact much greater than, 100. Target rating points express the same concept, but with regard to a more narrowly defined target audience. [1] [2]GRPs are used predominantly as a measure of media with high potential exposures or impressions. Purpose [ edit]The purpose of the GRP metric is to measure impressions in relation to the number of people in the target for an advertising campaign. [1] GRP values are commonly used by media buyers to compare the advertising strength of components of a media plan. Construction [ edit]GRPs are most directly calculated by summing the ratings of individual ads in a campaign. If a television program has an average rating of 7, and an ad is placed on 5 episodes, then the campaign has 7 × 5 = 35 GRPs. GRPs are simply total impressions related to the size of the target population: GRPs (%) = 100 * Impressions (#) ÷ Defined population (#) [1]GRPs can also be related to measures of the reception of the ad campaign. If an ad campaign results in 50% of the target seeing the advertising 3 times on average, then the campaign's size was 150 GRPs: GRPs (%) = 100 * Reach (%) × Average frequency (#)References [ edit]^ a b c Farris, Paul W.; Neil T. Bendle; Phillip E. Pfeifer; David J. Reibstein (2010). Marketing Metrics: The Definitive Guide to Measuring Marketing Performance. Upper Saddle River, New Jersey: Pearson Education, Inc. ISBN 0-13-705829-2. The Marketing Accountability Standards Board (MASB) endorses the definitions, purposes, and constructs of classes of measures that appear in Marketing Metrics as part of its ongoing Common Language in Marketing Project.^ American Marketing Association Dictionary. "Archived copy". Archived from the original on 2012-11-21. Retrieved 2012-11-29.. Retrieved 2013-2-11. The Marketing Accountability Standards Board (MASB) endorses this definition as part of its ongoing Common Language in Marketing Project. Categories: Marketing performance measurement Marketing terminology  Noise - Basic Information Noise - Basic Information CLOSE ALLWhat are sound and noise? Sound is what we hear. Noise is unwanted sound. The difference between sound and noise depends upon the listener and the circumstances. Rock music can be pleasurable sound to one person and an annoying noise to another. In either case, it can be hazardous to a person's hearing if the sound is loud and if he or she is exposed long and often enough. Sound is produced by vibrating objects and reaches the listener's ears as waves in the air or other media. When an object vibrates, it causes slight changes in air pressure. These air pressure changes travel as waves through the air and produce sound. To illustrate, imagine striking a drum surface with a stick. The drum surface vibrates back and forth. As it moves forward, it pushes the air in contact with the surface. This creates a positive (higher) pressure by compressing the air. When the surface moves in the opposite direction, it creates a negative (lower) pressure by decompressing the air. Thus, as the drum surface vibrates, it creates alternating regions of higher and lower air pressure. These pressure variations travel through the air as sound waves ( Figure 1 ). Figure 1Table 1 lists the approximate velocity of sound in air and other media. In gases, the higher the velocity of sound, the higher the pitch will be (Remember the "Mickey Mouse" sound when people talk after inhaling helium gas?). Table 1 Approximate Speed of Sound in Common Materials Medium Sound Velocity (ft/s) m/s Air, dry (0°C and 760 mm Hg) 1,100 330Wood (soft - along the fibre) 11,100 3,400Water (15°C) 4,700 1,400Concrete 10,200 3,100Steel 16,000 5,000Lead 3,700 1,200Glass 18,500 5,500Hydrogen (0°C and 760 mm Hg) 4,100 1,260The hearing mechanism of the ear senses the sound waves and converts them into information which it relays to the brain. The brain interprets the information as sound. Even very loud sounds produce pressure fluctuations which are extremely small (1 in 10,000) compared to ambient air pressure (i.e., atmospheric pressure). The hearing mechanism in the ear is sensitive enough to detect even small pressure waves. It is also very delicate: this is why loud sound may damage hearing. Why is noise an important workplace hazard? Noise is one of the most common occupational health hazards. In heavy industrial and manufacturing environments, as well as in farms, cafeterias, permanent hearing loss is the main health concern. Annoyance, stress and interference with speech communication are the main concerns in noisy offices, schools and computer rooms. To prevent adverse outcomes of noise exposure, noise levels should be reduced to acceptable levels. The best method of noise reduction is to use engineering modifications to the noise source itself, or to the workplace environment. Where technology cannot adequately control the problem, personal hearing protection (such as ear muffs or plugs) can be used. Personal protection, however, should be considered as an interim measure while other means of reducing workplace noise are being explored and implemented. As a first step in dealing with noise, workplaces need to identify areas or operations where excessive exposure to noise occurs. How can I tell if my workplace is too loud? If you answer yes to any of the following questions, the workplace may have a noise problem. Do people have to raise their voices? Do people who work in noisy environments have ringing in their ears at the end of a shift? Do they find when they return home from work that they have to increase the volume on their car radio higher than they did when they went to work? Does a person who has worked in a noisy workplace for years have problems understanding conversations at parties, or restaurants, or in crowds where there are many voices and "competing" noises? If there is a noise problem in a workplace, then a noise assessment or survey should be undertaken to determine the sources of noise, the amount of noise, who is exposed and for how long. What are some properties of noise that can be measured? The properties of noise which are important in the workplace are:frequencysound pressuresound powertime distribution What are pitch and frequency? Frequency is the rate at which the source produces sound waves, i.e. complete cycles of high and low pressure regions. In other words, frequency is the number of times per second that a vibrating body completes one cycle of motion. The unit for frequency is the hertz (Hz = 1 cycle per second: Figure 1 shows one cycle from an air compression to a minimum pressure and back to a maximum pressure). The Harvard Dictionary of Music defines the pitch as a "stretch of sound whose frequency is clear and stable enough to be heard as not noise". The Oxford Dictionary defines pitch as "the quality of a sound governed by the rate of vibrations producing it; the degree of highness or lowness of a tone." Since the pitch is determined mostly by frequency, it is usually identified with it. The pitch depends also, in a lower degree, on the sound level and on the physiology of the auditory system. Low pitched or bass sounds have low frequencies. High-pitched or treble sounds have high frequencies. A healthy, young person can hear sounds with frequencies from roughly 20 to 20,000 Hz. The sound of human speech is mainly in the range 300 to 3,000 Hz. What is sound pressure? Sound pressure is the amount of air pressure fluctuation a noise source creates. We "hear" or perceive sound pressure as loudness. If the drum in our example ( Figure 1) is hit very lightly, the surface moves only a very short distance and produces weak pressure fluctuations and a faint sound. If the drum is hit harder, its surface moves farther from its rest position. As a result, the pressure increase is greater. To the listener, the sound is louder. Sound pressure also depends on the environment in which the source is located and the listener's distance from the source. The sound produced by the drum is louder two metres from the drum if it is in a small bathroom, than if it is struck in the middle of a football field. Generally, the farther one moves from the drum, the quieter it sounds. Also if there are hard surfaces that can reflect the sound (e.g., walls in a room), the sound will feel louder than if you heard the same sound, from the same distance, in a wide-open field. Sound pressure is usually expressed in units called pascals (Pa). A healthy, young person can hear sound pressures as low as 0.00002 Pa. A normal conversation produces a sound pressure of 0.02 Pa. A gasoline-powered lawn mower produces about 1 Pa. The sound is painfully loud at levels around 20 Pa. Thus the common sounds we hear have sound pressure over a wide range (0.00002 Pa - 20 Pa). What is a sound pressure level? It is difficult to work with the broad range of common sounds pressures (0.00002 Pa - 20 Pa). To overcome this difficulty we use decibel (d B, or tenth (deci) of a Bel)). The decibel or d B scale is more convenient because it compresses the scale of numbers into a manageable range. The decibel is named after Alexander Graham Bell, the Canadian pioneer of the telephone who took great personal interest in the problems of deaf people. Sound pressure converted to the decibel scale is called sound pressure level (Lp). Appendix A gives a detailed explanation of decibels and sound pressure levels. Figure 2 compares sound pressures in pascals and sound pressure levels in decibels (d B). The zero of the decibel scale (0 d B) is the sound pressure of 0.00002 Pa. This means that 0.00002 Pa is the reference sound pressure to which all other sound pressures are compared on the d B scale. This is the reason the decibels of sound are often indicated as d B re 0.00002 Pa. Figure 2What is sound power? The sound power is the sound energy transferred per second from the noise source to the air. A noise source, such as a compressor or drum, has a given, constant sound power that does not change if the source is placed in a different environment. Power is expressed in units called watts (W). An average whisper generates a sound power of 0.0000001 watts (0.1 microwatt (µW)), a truck horn 0.1 W, and a turbo jet engine 100,000 W. Like sound pressure, sound power (in W) is usually expressed as sound power levels in d B. Appendix B provides examples of sound power level calculations. Figure 3 relates sound power in watts to sound power level in decibels. Note that while the sound power goes from one trillionth of a watt to one hundred thousand watts, the equivalent sound power levels range from 0 to 170 d B. Figure 3What is the relation between sound pressure and sound power? Because the sound power of a noise source is constant and specific, it can be used to calculate the expected sound pressure. The calculation requires detailed information about the noise source's environment. Usually a noise source with a lower sound power generates less sound pressure. For example, from the sound power of a compressor, one can calculate the expected sound pressure and sound pressure level at a certain location and distance. This information can be helpful in determining possible noise exposures and how they compare to the noise guidelines. The manufacturer can often provide noise emission data such as sound pressure levels under standard conditions and the sound power of equipment. A number of international standards are available for labelling machines and equipment with their noise emission levels. In Canada, the CSA Standard Z107.58 Noise Emission Declarations for Machinery provides manufacturers with a means to determine and to create noise emission declarations for the machinery they produce. In addition, Health Canada has issued a notice to stakeholders recommending that this noise data be included in the technical sales literature and instructions for use of machinery intended for a workplace. What kinds of noise are there? Noise can be continuous, variable, intermittent or impulsive depending on how it changes over time. Continuous noise is noise which remains constant and stable over a given time period. The noise of boilers in a power house is relatively constant and can therefore be classified as continuous. Most manufacturing noise is variable or intermittent. Different operations or different noise sources cause the sound changes over time. Noise is intermittent if there is a mix of relatively quiet and noisy periods. Impulse or impact noise is a very short burst of loud noise which lasts for less than one second. Gun fire or the noise produced by punch presses are examples of such noise. What are A-weighted decibels? The sensitivity of the human ear to sound depends on the frequency or pitch of the sound. People hear some frequencies better than others. If a person hears two sounds of the same sound pressure but different frequencies, one sound may appear louder than the other. This occurs because people hear high frequency noise much better than low frequency noise. Noise measurement readings can be adjusted to correspond to this peculiarity of human hearing. An A-weighting filter which is built into the sound measuring instrument de-emphasizes low frequencies or pitches. Decibels measured using a sound meter equipped with this filter are A-weighted and are called d B (A). Legislation on workplace noise normally gives exposure limits in d B (A). Table 2 lists examples of typical noise levels. A-weighting serves two important purposes:gives a single number measure of noise level by integrating sound levels at all frequenciesgives a scale for noise level as experienced or perceived by the human ear Table 2 Typical Noise Levels Noise Source d B (A)pneumatic chipper at 1 metre 115hand-held circular saw at 1 metre 115textile loom 103newspaper press 95power lawn mower at 1 metre 92diesel truck 50 km per hour at 20 metres 85passenger car 60 km per hour at 20 metres 65conversation at 1 metre 55quiet room 40What are basic rules of working with decibel (d B) units? The decibel [d B, and also d B (A)] is a logarithmic scale. For mathematical calculations using d B units, we must use logarithmic mathematics (see Appendix A ). However, in our day-to-day work we do not need such calculations. The use of d B unit makes it easy to deal with the workplace noise level data provided we use a set of simple rules as summarized in Table 3. Table 3 Decibel (d B) basics Change in d B Change in sound energy3 d B increase Sound energy doubled3 d B decrease Sound energy halved10 d B increase Sound energy increased by factor of 1010 d B decrease Sound energy decreased by factor of 1020 d B increase Sound energy increased by factor of 10020 d B decrease Sound energy decreased by factor of 100How are noise levels added? Sound pressure levels in decibels (d B) or A-weighted decibels [d B (A)] are based on a logarithmic scale (see Appendix A ). They cannot be added or subtracted in the usual arithmetical way. If one machine emits a sound level of 90 d B, and a second identical machine is placed beside the first, the combined sound level is 93 d B, not 180 d B. Table 4 shows a simple way to add noise levels. Table 4 Addition of Decibels Numerical difference between two noise levels [d B (A)] Amount to be added to the higher of the two noise levels [d B or d B (A)]0 3.00.1 - 0.9 2.51.0 - 2.4 2.02.4 - 4.0 1.54.1 - 6.0 1.06.1 - 10 0.510 0.0Step 1: Determine the difference between the two noise levels and find the corresponding row in the left hand column. Step 2: Find the number [d B or d B (A)] corresponding to this difference in the right hand column of the table. Step 3: Add this number to the higher of the two decibel levels. For instance, using the example of two machines each emitting a noise level of 90 d B: Step 1: The numerical difference between the two levels is 0 d B (90-90= 0), using the first row. Step 2: The number corresponding to this difference of 0, taken from the right hand column, is 3. Step 3: Add 3 to the highest level, in this case 90. Therefore, the resulting noise level is 93 d B. When the difference between two noise levels is 10 d B (A) or more, the amount to be added to the higher noise level is zero. In such cases, no adjustment factor is needed because adding in the contribution of the lower in the total noise level makes no perceptible difference in what people can hear or measure. For example if your workplace noise level is 95 d B (A) and you add another machine that produces 80 d B (A) noise, the workplace noise level will still be 95d B (A). Appendix A - Sound Pressure Level Calculations Sound pressure level in decibels is defined in the following way:d B = 20 log (Sound Pressure/Reference Pressure)The "log" or logarithm of a number is a mathematical manipulation of the number, based on multiples of 10. It is the exponent that indicates the power to which the number 10 is raised to produce a given number. For example, the logarithm of 10 is 1 since 10 is multiplied by itself only once to get 10. Similarly, the logarithm of 100 is 2 since 10 times 10 is 100. The logarithm of 1000 is 3 since 10 times 10 times 10 is 1000. Thereforelog (1) = 0 Since 10 to the exponent 0 = 1,log (10) = 1 since 10 to the exponent 1 = 10,log (100) = 2 since 10 to the exponent 2 = 100,log (1000) = 3 since 10 to the exponent 3 = 1000The logarithm scale simply compresses the large span of numbers into a manageable range. In other words, the scale from 10 to 1000 is compressed, by using the logarithms, to a scale of 1 to 3. The decibel scale for sound pressures uses as the reference pressure the lowest noise that the healthy young person can hear (0.00002 Pa). It divides all other sound pressures by this amount when calculating the decibel value. Sound pressures converted to the decibel scale are called sound pressure levels, abbreviated Lp. So, the sound pressure level of the quietest noise the healthy young person can hear is calculated in this way: Lp = 20 log ( 0.00002/ 0.00002) = 20 log (1) = 20 X 0 = 0 d BThe sound pressure level or Lp in a very quiet room, where the sound pressure is 0.002 Pa, is calculated: Lp = 20 log (0.002/ 0.00002) = 20 log (100) = 20 X 2 = 40 d BThe sound pressure level of a typical gasoline-powered lawn mower, which has a sound pressure of 1 Pa, is calculated Lp = 20 log (1/0.00002) = 20 log (50 000) = 20 X 4.7 = 94 d BAppendix B - Sound Power Level Calculations Sound power levels or Lw are determined by the following formula: Lw = 10 log (Sound Power Level / Reference Power Level )The reference power is one trillionth of a watt (0.000000000001 W). Therefore Lw = 10 log (Sound Power Level / 0.000000000001)Thus, the sound power level associated with an average whisper, which has a sound power of 0.0000001 W, is calculated Lw = 10 log (0.0000001/ 0.000000000001) = 50 d BDocument last updated on March 5, 2014  Noise FAQs Noise FAQs How is noise measured? How are noise level changes perceived? How do changes in traffic or roadway geometry affect noise levels? When is a noise analysis required? Is a noise analysis required when the speed limit of a highway is changed? Does CDOT analyze noise levels on existing highways? What constitutes a traffic noise impact? How was the selection of the noise levels in the Noise Abatement Criteria determined? Does EPA have standards which apply to highway noise? What does CDOT consider "feasible and reasonable"? What is a "substantial noise reduction"? What types of noise barriers are constructed? How do noise barriers work? Are noise barriers built to protect locations on the upper floors of homes? How are noise reflections from buildings and barrier walls considered? Will planting vegetation help reduce noise levels? Can anything be done about “Jake Brake” use? What is the effect of pavement type on noise levels? Typical Noise Levels Q: How is noise measured? A: Noise, usually defined as unwanted or unacceptable sound, is measured in terms of decibels. A decibel is a unit of measurement that quantifies the sound pressure differences in the air that we perceive as sound (or noise) on a scale ranging from zero decibels on up. Zero decibels is the threshold of human hearing, 40 to 50 decibels is normal for a peaceful neighborhood, 70 to 80 decibels is the level adjacent to a busy urban street or 50 feet from a major freeway, and 120 to 140 decibels is a typical level at which sound is painful. For highway traffic noise studies, noise levels are quantified in terms of the equivalent sound level, or Leq. The Leq is essentially the average noise level over period of time, usually one hour. Q: How are noise level changes perceived? A: Studies have shown that changes in noise levels of 3 decibels or less are not normally detectable by the average human ear. An increase of 5 decibels is generally readily noticeable by anyone, and a 10-decibel increase is usually felt to be "twice as loud" as before. Q: How do changes in traffic or roadway geometry affect noise levels? A: Due to the nature of the decibel scale, a doubling of traffic will result in a 3-decibel increase in noise levels, which in and of itself would not normally be a perceivable noise increase. Traffic would need to increase at least three times to result in a readily perceivable (5 decibel) increase in noise. Using the same reasoning, if a highway is moved half as close to existing homes as it is now (i.e., from 200 to 100 feet), the noise levels will increase by 3 decibels. Conversely, if a highway is moved double the distance from existing homes, the noise levels will decrease by 3 decibels. Noise level increases due to highway projects are usually due to a combination of increased traffic and changes in the roadway alignment. Q: When is a noise analysis required? A: A noise analysis is required for a proposed CDOT project if that project consists of: · A new highway built on a new location, interchange modifications, or an existing highway that is significantly altered by substantially changing the horizontal or vertical characteristics of the road, or the number of through traffic lanes being increased or auxiliary lanes added. Minor projects, such as normal roadway resurfacings (without adding new lanes), do not require a noise analysis. Noise analysis is also required if there is an addition of a new, or a substantial alteration of an existing, a weigh station, rest stop, ride-share lot, or toll plaza. Q: Is a noise analysis required when the speed limit of a highway is changed? A: No. Under the current regulations, a speed limit increase does not qualify as a project in which a noise analysis is required. CDOT does not have legal enforcement authority on the highways and cannot enforce lower speeds; enforcement of the traffic laws are the responsibility of local law enforcement. Q: Does CDOT analyze noise levels on existing highways? A: In the absence of a major highway project as described above, CDOT does not perform noise studies or mitigate noise for existing highways. Q: What constitutes a traffic noise impact? A: A "noise sensitive receiver" (defined as homes, parks, schools, businesses, etc.) is considered impacted by noise if either future noise levels (generally a 20 year projection) approach or exceed the CDOT Noise Abatement Criteria, or if there is a substantial increase in future noise levels over existing noise levels from a proposed CDOT project as described above. These are the noise levels experienced at the commonly used exterior portions of a property on the lowest or ground level for each home or individual unit. For residences, schools, and parks, impact is defined when the Leq is 66 decibels or higher, and for noise sensitive businesses the impact Leq value is 71 decibels. A substantial increase impact occurs when there is a projected 10-decibel increase over existing noise levels. Impacts such as these require mitigation consideration and analysis, which will result in the construction of noise barriers if they are determined to be feasible and reasonable. Q: How was the selection of the noise levels in the Noise Abatement Criteria determined? A: CDOT's selection of the noise abatement criteria levels were based on guidance from FHWA, and is consistent with the criteria used by all state DOT's. FHWA used numerous approaches in establishing the noise abatement criteria were considered, to include hearing impairment, annoyance, sleep interference, and speech communication interference. The main challenge in establishing the criteria was to balance noise levels which are desirable with those that are achievable. As a result, speech impairment was usefully applied as being the condition that best met that balance. Q: Does EPA have standards which apply to highway noise? A: Not at this time. EPA does have recommended noise levels which are considered goals, but did not recommend those levels as strict standards applicable to highway projects due to factors including but not limited to cost, engineering feasibility, and geographical characteristics. Q: What does CDOT consider "feasible and reasonable"? A: A noise barrier must be both feasible and reasonable if it is to be constructed with a highway project. Feasibility and reasonableness are determined by criteria that are quantifiable. As a result, noise mitigation is not automatically provided where noise impacts have been identified. A barrier is feasible if it can be constructed without major engineering or safety issues and provide a substantial noise reduction to the adjacent receivers. Reasonableness deals with whether the barrier can be designed to achieve a noise reduction design goal of 7 decibels, whether the barrier can be constructed in a cost-efficient manner, and the desires of the community. All 3 of these criteria must be met for a barrier to be considered reasonable to build. Q: What is a "substantial noise reduction"? A: A noise barrier must provide at least a readily perceptible decrease in noise levels to adjacent receivers to be feasible. This is defined as a noise decrease of at least 5 decibels. As noise level changes of 3 decibels or less are not generally perceivable, it is not prudent to construct a noise barrier that gives only a 1 or 2 decibel benefit to adjacent properties. Q: What types of noise barriers are constructed? A: Noise barriers are commonly constructed as walls, earthen berms, or a combination of the two. Walls are most common, and are usually constructed out of dense materials such as concrete or masonry block. Earth berms are a natural alternative to walls, but require much more land to construct. Walls can be constructed on top of berms in order to raise the overall height of the barrier. Q: How do noise barriers work? A: Noise barriers reduce noise by blocking the direct travel of sound waves from a source (such as a highway) to adjacent homes or businesses, forcing the waves over the top or around the barrier. The barrier must be high enough and long enough to block the view (line of sight) of the highway. This is the phenomenon that allows a noise barrier to provide a perceivable noise reduction. Noise barriers do very little good for homes on a hillside overlooking a road or for buildings which rise above a barrier. Openings or gaps in barriers for driveway connections or street intersections reduce barrier effectiveness. Noise barriers are most effective for the first one or two rows of homes at distances up to 200 to 300 feet from the barrier. As noise levels decrease with distance, there is a point away from the highway at which noise barriers are no longer effective. It is important to note that barriers are not designed to eliminate or block all noise. Q: Are noise barriers built to protect locations on the upper floors of homes? A: Noise barriers may, under certain geographic conditions, be able to be designed to protect upper levels of multi-family structures, where each unit is a separate residence. For single-family homes, the primary consideration is the outdoor, ground-floor areas of human activity. Barriers built for the second floor would have to be tall enough to provide a substantial noise reduction for those areas, which in most cases would require very high walls that would not be feasible or reasonable. Q: How are noise reflections from buildings and barrier walls considered? A: Highway traffic noise levels are not substantially increased by construction of a noise barrier or the presence of a building on the opposite side of a highway from sensitive properties. This is because the theoretical maximum noise increase from a source is limited to 3 decibels, which corresponds to a doubling of the source. In practice, not all of the sound energy is reflected back to the receiver. Some of the sound is diffracted over the barrier, some is reflected to points other than the affected property, some is scattered and/or absorbed by ground coverings and other terrain, and some is blocked by the presence of other vehicles on the highway. The overall noise increase is normally limited to 1-2 decibels at the most. In general, this is not a perceptible increase, but the character of the noise may seem to change, which is what is usually noticed. In the case of parallel barriers, however, studies have shown that if two walls are constructed very close together, there is a potential for multiple reflections that may perceptibly increase noise levels. Generally, this is not normally a problem for barriers greater than 200 feet apart or where the width-to-height ratio is more than 10:1 (barriers 10 feet high should be at least 100 feet apart). Q: Will planting vegetation help reduce noise levels? A: Vegetation is not effective for reducing noise levels. It is not feasible to plant enough vegetation along a highway to achieve reduction, although planting trees or shrubs can provide aesthetic benefit and visual screening. Q: Can anything be done about "Jake Brake" use? A: Colorado state law now requires that any vehicle equipped with engine compression brake devices (commonly referred to as "Jake Brakes") be equipped with proper mufflers. Failure to do so will result in a $500 fine. The enforcement of this law is the responsibility of the local authorities. CDOT has not restricted the use of these devices for safety reasons. However, CDOT has assisted local entities with this issue by installing "Engine Brake Mufflers Required" signs along selected highways. Q: What is the effect of pavement type on noise levels? A: Research regarding pavement influence on noise levels has been an ongoing process. In general, the use of certain types of asphalt pavements or texturing of concrete pavements can give an initial noise reduction benefit to properties 200 to 300 feet from the highway. Over a long period of time, however, it is not known if these benefits continue to be realized. As a result, pavement type, in and of itself, cannot be considered as an alternative to conventional noise mitigation measures at this time. CDOT's present policy for pavement type selection is made based on a life‐cycle cost analysis, which at this time does not consider noise as a primary factor. Typical Noise Levels Noise Source Noise Level (d BA)Commercial Jet 110-120Shouting at 5 feet 95-105Heavy Truck/Motorcycle at 25 feet 85-95Freeway Traffic at 50 feet 70-80Conversational Speech at 5 feet 55-65Quiet Neighborhood 45-55Living Room 35-45Remote Outdoor Location (no wind) 20-30Threshold of Hearing 0  What do âQRMâ and âQSBâ refer to? _Amateur Radio Stack Exchange is a question and answer site for amateur radio enthusiasts. Join them; it only takes a minute: Sign up Here's how it works: Anybody can ask a question Anybody can answer The best answers are voted up and rise to the top What do “QRM” and “QSB” refer to?up vote6down votefavorite An answer on Basic QSO format? mentions things like "QRM" and "QSB". What do those terms mean?q-codes jargonshare improve this questionedited Apr 13 '17 at 12:59Community ♦1asked Oct 23 '13 at 1:49Amber1,723 3 12 28add a comment1 Answer active oldest votesup vote8down voteaccepted"QRM" is one of many Q-codes used as abbreviations in radio communication. "QRM" in particular refers to human-generated interference (as opposed to "QRN" which is used to refer to atmospheric noise). "QSB" refers to fading (variation in signal strength over time). The codes originated from the desire to keep CW (morse code) transmissions as brief as possible due to the format's inherent bandwidth limits, but have stuck around and now often show up as abbreviations in regular conversation as well.share improve this answeranswered Oct 23 '13 at 1:49Amber1,723 3 12 28yeah, sorry; should've been clearer in my answer. – scruss Oct 23 '13 at 2:192No worries. I think there's a general tendency in the ham community to tend towards jargon; I just like to help make stuff more approachable for people who aren't as familiar with the lay of the land. – Amber Oct 23 '13 at 5:51add a comment Your Answer Sign up or log in Sign up using Google Sign up using Facebook Sign up using Email and Password Post as a guest Name Email By posting your answer, you agree to the privacy policy and terms of service. Not the answer you're looking for? Browse other questions tagged q-codes jargon or ask your own question.asked4 years, 5 months agoviewed9,007 timesactive4 years, 5 months ago Linked-1 Basic QSO format? 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Desktop Motherboard Find prime factors in C++Clown image in latex Prove no contraction in the orthogonal directions Story about arriving in hell and finding it emptyquestion feed  Decibel Range Charts and Hearing Info Decibel Range Charts and Hearing Info The charts on this page will show you different noise levels for specific jobs, tools, and various situations. The important thing to remember is to always protect your hearing for noise levels above 85 d B and use double protection if levels go over 105d B. Once your hearing has been damaged it can't be fixed... So wear hearing protection....unless you like the idea of wearing a hearing aid all the time!Decibel (d B) Range Charts - Click to Enlarge Decibel (d B) is the unit used to measure a sound's strength. The decibel scale is not linear but logarithmic. This means that noise levels can't be added directly like other numbers. On the decibel scale, the smallest audible sound (near total silence) is 0 d B. A sound 10 times more powerful is 10 d B. A sound 100 times more powerful than near total silence is 20 d B. A sound 1,000 times more powerful than near total silence is 30 d B. For example, a backhoe and a compressor each producing 90 d B have a combined output of 93 d B, not 180. But 93 d B is still twice as much noise as 90 d B. In other words, sound intensity doubles every 3 d B. Hearing protection should be used for any level over 85 d B and double protection for any level over 105 d B. Sounds must also be specified in terms of frequency or pitch. Most workplace noises include a wide band of frequencies and are measured through the "A" filter in sound-level meters. The noise level is therefore expressed in decibels (d B) on the "A" scale, or d B (A). Duration of exposure is equally important. Duration is typically measured over a workday and accumulated through many years. The chart below shows differenttypes of power tools and their noise levels. Always wear hearing protection for anything over 85 d B!HOW MUCH PROTECTION DO YOU NEED? USE THIS CHART TO WORK OUT THE CORRECT GRADE OF HEARING PROTECTION FOR YOUR WORKPLACE: HOW LOUD IS THE NOISE HAZARD DECIBELSTIME EXPOSED TO NOISE ALLOWABLE LEVEL NOISE LEVEL ABOVE LIMIT RECOMMENDED HEARING PROTECTION GRADEBELT SANDER 82-92 8 HOURS 85 d BA Up to 12 d BA Grade 2BAND SAW 94-95 4 HOURS 88 d BATRUCK/TRACTOR 90-110 2 HOURS 91 d BASKILL SAW/CHAIN SAW 95-110 I HOUR 94 d BA Up to 18 d BA Grade 3BAND SAW 94-95 30 MINS 97 d BAWOOD PLANER 94-96 15 MINS 100 d BABRAKE RIVETTER 97-99 8 MINS 103 d BA Up to 24 d BA Grade 4GRINDER 83-100 4 MINS 106 d BAROUTER 98-100 2 MINS 109 d BAGUILLOTINE 94-103 1 MIN 112 d BA Up to 30 d BA Grade 5WELDING MACHINE 99-100 30 SECS 115 d BACIRCULAR SAW 100-106IMPACT WRENCH 104-107DIESEL GENERATOR 107-111SAND BLASTING 105-115COMPRESSOR 101-123PNEUMATIC DRILL 120-130APPROVED HEARING PROTECTION GRADESHearing Protection Grade Equivalent Continuous Sound level (8 Hours) Types of Approved Hearing Protection1 86-91 d B (A) Earplugs/Earmuffs2 92-97 d B (A) Earplugs/Earmuffs3 98-103 d B (A) Earmuffs4 104-109 d B (A) Earmuffs5 110-115 d B (A) Earmuffs Normal Ear Function: Sound is transmitted as sound waves from the environment. The sound waves are gathered by the outer ear and sent down the ear canal to the eardrum. The sound waves cause the eardrum to vibrate, which sets the three tiny bones in the middle ear into motion. The motion of the bones causes the fluid in the inner ear or cochlea to move. The movement of the inner ear fluid causes the hair cells in the cochlea to bend. The hair cells change the movement into electrical pluses. These electrical impulses are transmitted to the hearing (auditory) nerve and up to the brain, where they are interpreted as sound.  Loudness From Wikipedia, the free encyclopedianavigation search For the Japanese band, see Loudness (band). The horizontal axis shows frequency in Hz In acoustics, loudness is the subjective perception of sound pressure. More formally, it is defined as, "That attribute of auditory sensation in terms of which sounds can be ordered on a scale extending from quiet to loud." [1] The relation of physical attributes of sound to perceived loudness consists of physical, physiological and psychological components. The study of apparent loudness is included in the topic of psychoacoustics and employs methods of psychophysics. In different industries, loudness may have different meanings and different measurement standards. Some definitions, such as ITU-R BS.1770 refer to relative loudness of different segments of electronically reproduced sounds, such as for broadcasting and cinema. Others, such as ISO 532A (Stevens loudness, measured in sones ), ISO 532B ( Zwicker loudness), DIN 45631 and ASA/ANSI S3.4, have a more general scope and are often used to characterize loudness of environmental noise. Loudness, a subjective measure, often confused with physical measures of sound strength such as sound pressure, sound pressure level (in decibels ), sound intensity or sound power. Filters such as A-weighting and LKFS attempt to compensate measurements to correspond to loudness as perceived by the typical human. Contents [ hide ]1 Explanation2 Hearing loss3 Compensation4 Normalization4.1 Broadcast4.2 Movie and home theaters4.3 Music playback5 Measurement6 See also7 Notes8 References Explanation [ edit]The perception of loudness is related to sound pressure level (SPL), frequency content and duration of a sound. [ citation needed] The relationship between SPL and loudness of a single tone can be approximated by Stevens's power law in which SPL has an exponent of 0.67. [a] More precise measurements indicate that loudness increases with a higher exponent at low and high levels and with a lower exponent at moderate levels. [ citation needed]The sensitivity of the human ear changes as a function of frequency, as shown in the equal-loudness graph. Each line on this graph shows the SPL required for frequencies to be perceived as equally loud, and different curves pertain to different sound pressure levels. It also shows that humans with normal hearing are most sensitive to sounds around 2–4 k Hz, with sensitivity declining to either side of this region. A complete model of the perception of loudness will include the integration of SPL by frequency. [2]Historically, loudness was measured using an "ear-balance" audiometer in which the amplitude of a sine wave was adjusted by the user to equal the perceived loudness of the sound being evaluated. Contemporary standards for measurement of loudness are based on summation of energy in critical bands. [3]Hearing loss [ edit]When sensorineural hearing loss (damage to the cochlea or in the brain) is present, the perception of loudness is altered. Sounds at low levels (often perceived by those without hearing loss as relatively quiet) are no longer audible to the hearing impaired, but sounds at high levels often are perceived as having the same loudness as they would for an unimpaired listener. This phenomenon can be explained by two theories, called "loudness recruitment" and "softness imperception". Loudness recruitment (LR) posits that loudness grows more rapidly for certain listeners than normal listeners with changes in level. This theory has been accepted as the classical explanation. Softness imperception (SI), a term coined by Mary Florentine around 2002, [4] proposes that some listeners with sensorineural hearing loss may exhibit a normal rate of loudness growth, but instead have an elevated loudness at their threshold. That is, the softest sound that is audible to these listeners is louder than the softest sound audible to normal listeners. Compensation [ edit]Main article: Loudness compensation The "loudness" control on some consumer stereos alters the frequency response curve to correspond roughly with the equal loudness characteristic of the ear. [5] Loudness compensation is intended to make the recorded music sound more natural when played at a lower levels by boosting low frequencies, to which the ear is less sensitive at lower sound pressure levels. Normalization [ edit]Loudness normalization is a specific type of audio normalization that equalizes perceived level such that, for instance, commercials do not sound louder than television programs. Loudness normalization schemes exist for a number of audio applications. Broadcast [ edit]Commercial Advertisement Loudness Mitigation Act European Broadcasting Union R128 [6]Movie and home theaters [ edit]Dialnorm Music playback [ edit]Sound Check in i Tunes Replay Gain Measurement [ edit]Historically Sone (loudness N) and Phon (loudness level L) units have been used to measure loudness. A-weighting follows human sensitivity to sound and describes relative perceived loudness for at quiet to moderate speech levels, around 40 phons. However, physiological loudness perception is a much more complex process than can be captured with a single correction curve. [2] Not only do equal-loudness contours vary with intensity, but perceived loudness of a complex sound depends on whether its spectral components are closely or widely spaced in frequency. When generating neural impulses in response to sounds of one frequency, the ear is less sensitive to nearby frequencies, which are said to be in the same critical band. Sounds containing spectral components in many critical bands are perceived as louder, even if the total sound pressure remains constant. Relative loudness monitoring in production is measured in accordance with ITU-R BS.1770 in units of LKFS. [7]Work began on ITU-R BS.1770 in 2001 after 0 d BFS+ level distortion in converters and lossy codecs had become evident; and the original Leq (RLB) loudness metric was proposed by Gilbert Soulodre in 2003. [8]Based on data from subjective listening tests, Leq (RLB) was compared against numerous other algorithms where it did remarkably well. [ why?] After modification of the frequency weighting, the measurement was made multi-channel ( monaural to 5.1 surround sound ). CBC, Dolby and TC Electronic and numerous broadcasters contributed to the listening tests. To make the loudness metric cross-genre friendly, a relative measurement gate was added. This work was carried out in 2008 by the EBU. The improvements were brought back into BS.1770-2. ITU subsequently updated the true-peak metric (BS.1770-3) and added provision for more audio channels, for instance 22.2 surround sound (BS.1770-4). See also [ edit]Loudness war Sending loudness rating Volume in acoustics is related to: Amplitude Sound pressure Dynamics LKFS, loudness standard for broadcast television and radio (also known as LUFS)Notes [ edit]^ The relationship between loudness and energy intensity of sound can therefore be approximated by a power function with an exponent of 0.3. References [ edit]^ American National Standards Institute, "American national psychoacoustical terminology" S3.20, 1973, American Standards Association.^ a b Olson, Harry F. (February 1972). "The Measurement of Loudness" (PDF). Audio: 18–22.^ As described in IEC 532, DIN 45631 and ASA/ ANSI S3.4^ Mary Florentine (March 2003), It's not recruitment-gasp!! It's softness imperception, 56 (3), Hearing Journal, pp. 10, 12, 14, 15, doi: 10.1097/01. HJ.0000293012.17887.b4^ Lenk, John D. (1998). Circuit Troubleshooting Handbook. Mc Graw-Hill. p. 163. ISBN 0-07-038185-2.^ EBU Recommendation R 128: Loudness normalisation and permitted maximum level of audio signals (PDF), European Broadcasting Union, August 2011, retrieved 2013-04-22^ Recommendation BS.1770, International Telecommunication Union, August 2012, retrieved 2013-05-31^ "Leq Meter". Retrieved 2015-12-15. [ hide]v t e Timbre Colors of noise Fundamental frequency Jivari Loudness Microinflection Noise Overtone Pitch Rustle noise Sawari Spectral envelope Sympathetic string Tonality Waveform Categories: Elements of music Acoustics 