An Inside Look at Cables and Connectors

Joe McCleskey
November 1999

Visit any place where video editors work and you'll likely find more than your share of cables: S-video cables, audio cables, power cables, composite video cablxes, headphone cables, microphone cables and cables for cable TV reception, among others. And if the cables aren't confusing enough for you, there's a whole host of connectors to go with them, with names like BNC, DIN, RCA, phone, phono, XLR and stereo mini-plug.

In this article, we're going to take an in-depth look at some of the cables commonly used for video. We'll take a look inside the four main cable types that home video producers deal with: composite (RCA-style) cables, S-video cables, RF cables and DV (IEEE 1394) cables.

Composite cables are perhaps the most commonly encountered cable type in consumer video. They often come in the box with home VCRs and camcorders. Sometimes, they come in groups of three attached cables--one with yellow RCA-style connectors for video and two with red and white connectors for stereo audio. Also included in this category are those cables that have yellow, red and white plugs on one end and a mini-plug connector on the other end. This type of cable often comes packaged with miniature camcorders that make use of the single connector on the camera body.

Often, video gear (especially professional video gear) will have BNC (bayonet nut coupling) connectors for composite video. The chief advantage of the BNC connector is its ability to lock in place with a push and a twist; this prevents connections from wiggling loose, a common problem with the typical RCA-style connectors.

On the video side, these cables carry composite signals, so called because the signal is a composite (or mixture) of all black-and-white and color information contained in the video signal. They usually consist of two wires running parallel to one another down the cable; one wire (power) corresponding to the tip of the connector and the other wire (ground) corresponding to the outside ring portion of the connector.

Why aren't these cables just called video cables? Because they actually carry two separate signals that are composited into one. Inside your camcorder and/or VCR, the black and white (luminance) information is dealt with separately from the color (chrominance) information. Back when television technology was black and white only, the only type of video signal a television had to cope with was a black and white signal. When color came along later, it was dealt with as another layer of information on top of the black and white signal, in order to make color TV signals compatible with existing black and white televisions.

To send both chrominance and luminance information together on the same cable, the two signals must be mixed together in a process known as modulation. The modulation of the signals--and subsequent de-modulation at the other end--is what makes the composite video signal highly susceptible to generation loss (the tendency of a signal to degrade whenever you make copies of it). The only type of video cables that are more susceptible to generation loss are the RF cables used for cable television and antenna hook-up.

RF cables gave cable television its name. The ubiquitous RF cable can be found mostly on television sets and VCRs, as well as a few old-school camcorders. RF stands for radio frequency. The name is appropriate because this is the cable most commonly used to transfer radio-frequency signals from an antenna to the VCR or TV set--or even from the cable TV station to your house.

RF cables are generally made of coaxial cable, a cable that carries two metal leads, one inside the other. The two wires do not carry two different signals; instead, they carry the power and ground for a single signal, with the ground (outside) cable providing limited shielding from radio interference.

The RF cable (sometimes referred to as an F cable) provides the best means of long-distance signal transfer. This is why it's most commonly used to connect cable TV stations to clients; with a heavily shielded cable and amplifiers in far-away neighborhoods, it's possible to send an RF signal miles and miles without serious degradation. However, it is the worst solution for making copies or editing. Here's why: remember how we told you that composite video signals mix the color and black-and-white signals into one? Well, the RF cable does this one better: it carries monaural audio along with the mixed color/black-and-white video signal. This means that problems arising from modulation/demodulation of the signal are multiplied in RF cables. Generation loss accrues at a much faster rate and even second-generation copies tend to have an abundance of video noise, audio noise and bleeding colors.

Camcorder enthusiasts who have television sets without composite video inputs (yes, they do still exist) must find some way to connect the video outputs of their camcorder to the RF-style connectors of their TV. VCRs usually provide the needed connections, but for some who still have older VCRs without video connectors, the RF-to-composite connection may require a separate inexpensive device called a modulator, readily available at consumer electronics outlets. Unfortunately, you can't just whip up an adapter to connect composite cables directly to RF cables without a modulator, because RF cables transmit signals differently than composite cables.

In short, you should only use RF cables for viewing video and use some other type of cable for copying and editing.

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