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HDTV FAQs - What is the Difference Between Digital TV and Analog TV?

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Although television transmission transitioned from analog to digital in the U.S. on June 12, 2009, there are still consumers that may be watching the few remaining low-power analog TV stations, subscribe to analog cable TV services, and/or continue to watch analog video sources, such as VHS, on either analog, digital, or HDTVs. As a result, the characteristics of analog TV are still an important factor to be aware of.

The difference between Analog TV and Digital TV has its roots in the way the TV signal is transmitted or transferred from the source to the TV, which, in turn, dictates the type of TV the consumer needs to use to receive the signal. This also applies to the way a DTV converter box has to transfer a signal to an analog TV, which is important for those consumers that use DTV converters to receive television programming on an analog TV set.

Before the DTV Transition was in place, standard analog TV signals were transmitted in a manner similar to radio.

In fact, the video signal of analog television was transmitted in AM, while the audio was transmitted in FM. Analog TV was subject to interference, such as ghosting and snow, depending on the distance and geographical location of the TV receiving the signal.

In addition, the amount of bandwidth assigned to an analog TV channel restricted the resolution and overall quality of the image. The analog TV transmission standard (in the U.S.) was referred to as NTSC.

NTSC is the U.S. standard that was adopted and came into popular use after World War II. NTSC is based on a 525-line, 60 fields/30 frames-per-second at 60Hz system for transmission and display of video images. This is an interlaced system in which each frame is scanned in two fields of 262 lines, which is then combined to display a frame of video with 525 scan lines.

This system works, but one drawback is that color TV broadcasting was not part of the equation when the system was approved. The implementation of color into the NTSC format has been a weakness of the system, thus the term for NTSC became known by many professionals as "Never Twice The Same Color". Ever notice that color quality and consistency varies quite a bit between stations?

Digital TV, or DTV, on the other hand, is transmitted as data bits of information, just as computer data is written or the way music is written on a CD. In this way, the signal is basically "on" or "off". In other words, the intent of DTV technology is that the viewer either sees an image or nothing at all. There is no gradual signal loss as distance from the transmitter increases. If the viewer is too far from the transmitter or is in an undesirable location, there is nothing to see.

On the other hand, unlike analog TV, digital TV has been designed from the ground up to take all the main factors of the television signal into consideration: B/W, color, and audio and can be transmitted as an interlaced (lines scanned in alternate fields) or progressive (lines scanned in linear sequence) signal. As a result, there is greater integrity and flexibility of signal content.

In addition, since the DTV signal is made up of "bits", the same bandwidth size that takes up a current analog TV signal, can accommodate not only a higher quality image in digital form, but the extra space not used for the TV signal can be used for additional video, audio, and text signals.

In other words, broadcasters can supply more features, such as surround sound, multiple language audio, text services, and more in the same space now occupied by a standard analog TV signal. However, there is one more advantage to the ability of a Digital TV channel's space; the ability to transmit a High Definition (HDTV) signal.

Lastly, another difference between Digital TV and Analog TV is the ability to broadcast programming in a true widescreen (16x9) format. The shape of the picture more closely resembles the shape of a movie screen, which enables the viewer to see the movie as the filmmaker intended. In Sports, you can get more of the action in one camera shot, such as viewing the entire length of a football field without making look like it is a long distance away from the camera.

A 16x9 TV can display widescreen images without a large amount of picture space taken up by black bars on the top and bottom of a widescreen image, which is what you see if such images are shown on a standard TV. Even non-HDTV sources, such as DVD can also take advantage of a 16x9 TV.

For a more detailed information on the widescreen aspect of digital TV, refer to my article Widescreen TV: the 16x9 Factor.

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