Composite video cables

Composite video was born back in 1953 with the advent of TV when it was necessary to compress all of the component video information into one signal for broadcast. That signal was designated ‘composite’ by the National Television Standards Committee (NTSC). It is comprised of three signals compressed into one. These are known as Y, U and Y, together referred to as YUV. Y is the brightness, while U and V represent hue and saturation and carry all the colour information required for the picture.

Everything that comes over the air to your TV antenna, or from your cable TV provider to your TV, or from the yellow video plug to your VCR, laserdisc or DVD is composite video. And all of these sources require some form of composite video cable to carry the signal from the source to your device.

Although composite video cables carry the simplest form of video signal, very often they are combined with a sound signal on a RF carrier and are most often associated by the distinctive yellow RCA connector. In fact, RCA cables have long been the most common format for composite video cables, despite the fact that poor impedance matching does not make them the ideal choice

Another reason composite video was ideal for TV was it was found that it could be directed at any broadcast channel simply by modulating the RF carrier frequency. Which is why most analogue home video equipment records in composite. In home applications such as recording from TV, or playing back to TV, RCA cables are normally used. BNC cable and coaxial cables are used in more professional applications. SCART cables have become the norm in Europe.

Composite video may be ideal as a broadcast medium but there are drawbacks. The device receiving the signal has to uncompress the data back into its components and since data is lost when the signal is compressed into composite, what you view is not the good as the original. The picture won’t be as crisp and the colours aren’t so rich.

Furthermore, modulating RF with the original video signal and then demodulating the signal back in the TV again causes further deterioration of the picture. Mixing various signals into the original composite causes significant problems. Most notably, dot crawl, due to cross talk between the colour and light portions of the signal. The solution to this was the introduction of the S-Video cable, which divided the light and colour into two separate signals.

DVDs, of course, don’t experience these problems as they are made up of component video, but this means that you shouldn’t use an RCA composite video cable to play a DVD on your TV as it downgrades the signal. An S-Video cable, while not a true composite video cable, is a much better choice,

It goes without saying that it is best to use component video cables where your devices support them. However, older devices may not have this capability, so in the event that you have to use composite video cables, it clearly makes sense to go for the high quality cables to minimise interference and loss of signal from composite video.