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What is "Analog" TV? Versus Digital?

Updated October 6, 2007

There is a widespread misconception within the general population that an "analog" TV is a CRT direct-view television and a "digital" TV is a flat-panel. You can't really blame anybody for thinking that, since the correct distinction is the difference between the old NTSC analog broadcast TV standard and our new ATSC digital standard. Unfortunately, most Americans have no idea we're getting a new digital TV standard, so that explains their confusion.

But apart from that, the term "analog" is still a mystery in this digital age.

Before there was "digital"--i.e. signals encoded in combinations of "1"s and "0"s, everything was analog, so there was no need to label anything as such. Sound traveling through air is an analog wave. The ripples radiating out from a pebble thrown into a pond are an analog signal.

Examples of early analog computers were mechanical adding machines (rather large contraptions filled with metal levers and cogs) and slide rules (the best made from bamboo), that would multiply to three decimal places of accuracy if your eyes were good, essentially by adding logarithms.

If any of this sounds familiar, you're dating yourself.

Our TV transition is all about how the TV signal is sent from the source to the TV transmitter, through the air via radio waves to your TV antenna, and into your TV's circuitry.

Under the old NTSC TV standard, the signal was analog--that is, transmitted in a wave form that if captured and displayed, would look like the little wavy electrical voltages that were produced by the camera sensors.

The tuners in "analog" TVs were therefore designed to select out ("tune") the signals being transmitted within a certain frequency range (channel) and send that signal to other parts of the TV circuit to control the electron beam "painting" the picture on your TV screen, and to drive the audio amplifier.

Pretty simple. And also susceptible to snow and ghosting, etc. when the signal became corrupted due to extraneous interference, signal reflections, and other unfavorable atmospheric conditions. Whatever hit your antenna, you saw on the screen.

Analog TV signals are also uncompressed. It takes a lot of bandwidth to send them on their way, or a big chunk of radio frequencies. Each TV channel uses 6 MHz of radio waves. The same channels are used for either analog or digital broadcasts.

Digital processors, by contrast, take the analog signal from the TV camera sensors and measure its electrical voltage (take a "sample") many times per second (60 times for video and thousands of times for audio), and converts those electrical measurements to numbers, which in turn are encoded as sets of "1"s and "0"s. The resulting digital description of the TV signal can be compressed (using MPEG-2 algorithms for broadcast TV signals) and sent over the air to your digital TV in that compressed digital stream of "1"s and "0"s.

Each pixel of a TV picture is created by combining three colors--red, green, and blue--and in digital TV each of these colors is described by 8-bits (a set of 8 "1"s and "0"s.)

Because its data stream is compressed, you can fit a digital high-definition TV signal (with five times the picture detail) in the same 6 MHz channel as one analog standard-definition signal. Or you can put five digital standard-definition signals (or sub-channels) into the same 6 MHz.

A "digital" TV, then, is one that has the circuitry built-in to receive and demodulate the broadcaster's digital signals. That is, it can uncompress and convert the "1"s and "0"s to a form that can be displayed. Since digital TVs are computers, they also do error-correction on the incoming signal, and may also do other signal processing to improve the picture.

Digital TVs can take the form of any display technology, including the traditional cathode ray tube (CRT) direct-view 4:3 television, as well as modern flat-panel sets. It's what's inside that counts, not what the outside looks like.

Widescreen vs. the old 4:3 squarish screen

Virtually all widescreen (16:9 aspect ratio) TVs are digital, but a 4:3 screen doesn't make a TV "analog."

There are still CRT TVs being made (with 4:3 screens), but they are now required to have digital receiver/demodulators (or "tuners") built in.

Mind you, there's nothing wrong with CRT direct-view sets, and you may find a couple of models with 16:9 widescreen displays left in stores. There is, however, something wrong with any new TV still having a 4:3 screen. Digital programming is all very quickly moving to the new widescreen format.

In the new digital era, 4:3 TVs will display programming in one of three ways: 1) letterboxed - with black bars on top and bottom, 2) centercut - with the sides of the picture chopped off so the screen is filled, or 3) postage stamped - an improperly encoded picture with black bars on all four sides.

None of which will make a camper happy.