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Glossary of Home Theater Terminology

Glossary of Audio, Video and Home Theater Terms


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AAC - Advanced Audio Coding. An audio codec used increasingly for downloaded music files, streaming-media, and satellite-radio applications.

AAD - Analog Analog Digital. A designation that indicates the recorded material was first recorded with analog equipment, then remixed on analog equipment and finally placed onto a digital recording medium.

AC - Alternating Current. The standard electrical current delivered to homes and businesses in the U.S. As opposed to DC - Direct Current.

AC-3 - The original named used for Dolby Digital. The name was later changed to feature the Dolby name.

Accuracy - When audio or video signals pass through a component, the signal may be changed slightly. The closer the output is to the original input, the greater the accuracy of the component.

Acoustic Suspension Speaker - A sealed-box speaker that uses the air behind the woofer to control cone movement.

Active Speaker - A speaker which includes an integral power amplifier to power or drive the speaker.

Active Scan Lines - The scan lines in a video frame that carry picture information rather than data for closed captioning or synchronization.

A/D - Analog to Digital. Refers to the conversion of analog sound or video to digital during storage, manipulation, or recording.

ADD - Analog Digital Digital. A designation that indicates the recorded material was first recorded with analog equipment, then remixed on digital equipment and finally placed onto a digital recording medium.

Adjacent Channel Selectivity - When tuning an FM station, the next station up or down the dial may interfere with the signal. A tuner's ability to reject those neighboring signals is measured by its selectivity.

ALiS - Alternate Lighting of Surfaces. An HD plasma panel technology designed to optimize performance when displaying 1080i material. Alternate rows of pixels are lit, similar to interlaced scanning. The resulting picture is bright, clear and improves the smoothness of movement as well extending the life of the plasma panel.

AM - Amplitude Modulation. The encoding of a signal into a radio wave by modulating its amplitude (the height of the wave). As opposed to FM, frequency modulation, wherein the frequency of the wave is modulated.

Amplifier - An audio component that takes line level audio inputs and increases the gain or level and outputs the signal to speakers. Amplifiers are used with other separate components or can be integrated together to make an Integrated Amplifier. Amplifiers are also available for other signals besides audio.

Analog - When a signal is continuously variable, it is analog. When a signal is broken into units that are rounded to discrete values, it is digital. Analog signals contain "all of the data" but it is prone to interference and degradation. It is not possible to catch and remove all of the interference from an analog signal and so the quality declines as it travels to your TV. With a digital signal, certain values are expected. When a value is received that is not within the expected range, it can be filtered or adjusted. This ability to detect and filter or repair a digital signal makes it possible to deliver a signal to your TV that is as good as when it left the studio.

Anamorphic - It is the preferred DVD format for widescreen (16:9) TVs because the image is restored to its widescreen format without any reduction in image quality. Anamorphic DVDs contain the highest level of resolution (460 to 480 lines) and thus yield the best picture quality. DVDs are often not labeled as anamorphic, so look also for the words "enhanced", " widescreen", "16:9". DVDs labeled "letterboxed" and in most cases "fullscreen" will have reduced image quality or even have some of the image edited to force it to fit a 4:3 screen. Anamorphic DVDs can be played on regular 4:3 TVs, but unless your TV or DVD player has a setting to vertically adjust the image, it will appear tall and thin.

ANSI Lumens - A standard for measuring the brightness of a projection TV. ANSI is the organization that set the standards for measurement. The IEC is now the organization setting the standard, but manufacturers are reluctant to switch, fearing consumer confusion.

Antenna - A device for transmitting or receiving signals. The size and shape of antennas are determined primarily by the frequency of the signal they are designed to receive. A high gain antenna is highly focused, whereas a low gain antenna receives or transmits over a wide angle.

Artifact - Any imperfection in a video image resulting from digital processing such as interlacing, up or down-conversion of the signal or conversion from a native to non-native format and vice-versa.

Aspect Ratio - Essentially the shape of the screen or image. It is the ratio of the width to the height. The standard square television screen is 4:3 or 1.33:1, while widescreen TV is 16:9 or 1.78:1. Most modern films are released in 1.85:1 or 2.35:1 aspects, which means that even on a widescreen TV the image will result in black bars at the top and bottom of the screen.

ATSC - Advanced Television Systems Committee. The organization that set the U.S. HDTV standards. It also refers to the TV channel tuner used to tune in HD signals. Compare to the NTSC which set the standard for pre HDTV signal and the tuner that tunes analog programming.

Attenuate - To decrease or otherwise reduce, as in to attenuate signal noise.

ATV - Advanced Television. The system and the standards defined by the ATSC.

Auto-Reverse - A feature that automatically reverses a tape when it reaches the end.

Auto-Rewind - A feature that automatically rewinds a tape to its beginning when it reaches the end.

A/V Receiver - Also called a Home Theater receiver, sometimes the term "integrated" is also used. Receivers take audio signals from components such as a CD player, tape deck and phonograph, amplify it and output it to the speakers. An A/V receiver is designed to also accept video inputs, such as from a DVD player, cable box and VCR, and output the signal to a television. In most cases the video signal is not processed but simply passed through to the TV. A/V receivers, in most cases, also have Dolby and DTS decoders to play multi-channel audio.

A/V Inputs - The connections on any component, such as a TV, receiver or VCR that enable connection to other output devices. The inputs often take the form of RCA jacks.

Audio outputs - An audio output is a connection (most often an RCA jack) on a device, such as a TV, that can be connected to a stereo or home theater system. A fixed output means the stereo is used to control the volume. A variable output means that the TV and the stereo can each control the volume.

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