There's a lot of electrical and magnetic interference in the air these days. Other power sources, appliances, close proximity to radio or TV stations-all these and more can create noise picked up by your cable unless properly shielded.

A shield is another conductive material, normally a metal foil or a wire mesh, that encircles and protects the integrity of your cable. It absorbs outside signals and/or reflects them back to the outside world. It also keeps your signal within your cable. The relationship between the conductor and shield within your cable can increase the Cable's capacitance. Once again, careful design is everything.

Audio and video signals are alternating current signals. They're similar to waves, like sine waves. For a wave to pass cleanly across a cable from one component to another, the impedance-or signal opposition-must be equal all the way across. The cable must be rated to carry signal at a certain impedance.

If the impedances do not match between signal source, cable and receiving component, the waves get out of phase and collide with each other. This actually reflects some of the power of the signal back to the source, causing noise and signal loss.

The more reflection, the less clean your signal, ultimately leading to loss of picture or color data. The video signal is a high frequency one, very susceptible to problems with impedance.

The video industry settled on a standard of 75 ohm impedance for video equipment. (Why did they choose this? Not one of our experts could say.)

"That 75 ohm impedance is most important in video," says Sands. "Most coaxial cable for ham or CB radio is 50, 52 or sometimes 100 ohms. In a coaxial cable there's a certain amount of resistance and capacitance per foot which impedes the signal. Using other than 75 ohm impedance cables will create problems like signal frequency loss and other distortions of the signal."

Pro cables are sold with the 75 ohm rating stamped on them. In the consumer industry, they're not marked; it's not a one-size-fits-all standard. You can't determine your cable's impedance without an expensive meter. So how do you know what you're getting?

"Ninety-five percent of the cables sold for video are 75 ohm cable," says Cornell. "In fact, I wouldn't be surprised to learn that all consumer audio and video RCA cables these days are 75 ohm impedance. The impedance is much less critical in consumer audio cabling, and it's probably easier for the consumer manufacturers to make one cable and label it two ways."

You've no doubt heard the term coaxial-coax for short-thrown about. Fancy word, simple concept: coax simply refers to any cable with a central wire surrounded by an insulator, a shield and a plastic outer jacket. if you've seen almost any kind of AV cable other than cheap speaker wire, you've seen coaxial cable.

"Today, 95 percent of the video and audio cable is coax," says Cornell.

That holds true even for Y/C cabling, the cables used for S-VHS and Hi8 equipment. Y/C cables actually have two small coaxial cables inside one jacket. Both are 75 ohm impedance.

Impedance plays a factor in audio cables, too. Pro audio cabling is usually designed for low impedance, balanced equipment. The audio cables included in most consumer camcorder accessory packs is for high impedance, unbalanced audio gear.

"Most pros use low impedance audio line, 600 ohm or less, and also use balanced lines," says Sands. "Balanced line is a three wire system. The signal on a balanced line is carried on two wires. The third is a ground and a shield. Balanced line can literally be run thousands of feet with little loss or noise pickup."

Regular unbalanced line is simply a shielded conductor; balanced cabling uses two conductors and a shield. Balanced audio equipment uses both conductors in a special arrangement to cancel out noise. The main difference between the two, aside from their connectors, is that only the latter has the ability to transmit your signal long distances without picking up external noise.

"Unbalanced line only has the two wires for the signal and should rarely be run more than 20 or 30 feet," says Sands. "I see an awful lot of people. like wedding videographers, running 50 feet or more of unbalanced audio cable and getting noise."