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What kind of cable should I buy?

The price of audio cables varies tremendously, so one obvious question is; what kind of audio cable do I actually need? The answer depends on the job it's being used for. Broadly speaking, you can divide audio cables into three categories depending on their use; cables designed for very low-level signals such as microphones, those designed for intermediate signal levels such as cd players or mixing desks ( so-called 'line level' signals) and cables designed for high-power applications, usually connecting amplifiers to loudspeakers. In addition to these categories there is a distinction between 'balanced' and 'unbalanced' connections.

Let's look first at cables designed for low-level signals. The main issue here is that these cables will almost always be used in an electro-magnetically 'noisy' environment, due both to all the electrical devices in use in the modern world as well as various natural sources. This 'noise' is generated by all electrical devices to some extent and any piece of wire that is exposed to it essentially acts as an aerial and picks some of it up; if the piece of wire is also carrying a signal the unwanted noise mixes with the wanted signal and degrades it.

This is particularly a problem with very low level signals as the undesired noise level can be quite high compared to the signal. Fortunately it is quite easy to screen out unwanted noise by encasing the wire in a shield ( or screen) of metal or other conductive material. Electromagnetic radiation will not pass through a conductive shield of this type ( as was demonstrated by Faraday with the Faraday cage), and so the noise is kept away from the signal. This is the principle of 'screened' or 'shielded' cables, and it is this that makes them essential for low-level signals.

A development of the simple screened audio cable is the 'balanced line'. Without going into too much technical detail, instead of using one wire for the signal and one for the screen, a balanced cable uses two wires for the signal (plus the screen, making three in total), connected in such a way that, when used with the correct equipment, any noise picked up on one wire is canceled out by the other wire. This gives an additional level of noise rejection even in very hostile environments, and is the standard for professional sound equipment. The usual connector for this kind of cable is the 3-pin XLR, but often a 3-pole ( sometimes known as 'stereo') jack is used as well. It should be noted though that this is not a stereo connection!

The balanced line is the best system to use wherever possible but you will only get the advantage if both the input and output devices (for example a microphone and a mixer) are 'balanced'. However for many domestic situations a conventional screened cable will be fine, particularly if the length of cable is fairly short.

Moving on to medium signal levels as found in cd players, mp3 players etc, here the quality of screening is somewhat less important as the level of the signal is relatively high compared to the level of any noise that is picked up. Generally balanced lines will only be found in professional equipment; domestic equipment almost universally uses conventional single screened cable.

Finally, with loudspeaker-level connections screening becomes unimportant as the signal level is many orders higher than any noise that might be picked up. Instead, as the cable can actually be required to pass quite a lot of power, the diameter of the wires becomes important, especially with longer cable runs and low-impedance loudspeakers as found in professional sound equipment..