by Miriam Kolar

Because they cancel out interference, BALANCED CABLES are generally effective in preserving the integrity of the audio signal. Connector plugs commonly used on balanced cables are XLR (3-prong mic connector) or TRS (Tip, Ring, Sleeve) 1/4" phone plugs. Balanced cables have one ground connection and two signal-carrying conductors ("leads") of equal potential but opposite polarity. This means that there is a "hot" or positive lead, and a "cold" or negative lead. Thus the audio signal is transmitted both in and out of phase (+ and -) at the same time. Both leads pick up hum interference, but this hum cancels out at the balanced input connection because it’s equivalent in its presence both in and out of phase.

Balanced cables can be either TWISTED-PAIR or NON-TWISTED PAIR; twisted-pair are more effective for hum reduction because both leads receive equivalent hum.

UNBALANCED CABLES have one conductor and a shield, and connect to unbalanced 1/4" phone plugs or RCA phono plugs. Because the signal is transmitted through both the lead and the shield, hum is received by both, at different levels. This difference in hum is amplified at the unbalanced input connection. Interference is therefore a problem in unbalanced cables, but the shorter the cable, the less hum introduced into the system.

How do I connect balanced and unbalanced gear?

Audio signals can flow between balanced and unbalanced gear. A BALANCED CABLE can be wired to an UNBALANCED CONNECTOR: To wire a 3-pin balanced mic cable to an unbalanced phone plug: the "hot" lead (red or white color-coded insulation) should be soldered to the phone-plug tip, the "cold" lead (black color-coded insulation) and the shield/ground should be soldered to the phone plug ground lug. Though this type of cabling is common, there is a better way to connect balanced and unbalanced gear. By using the physics of inductance and impedance matching you can turn a unbalanced -10dBV signal into a balanced +4dBU signal.

Is expensive shielded cable really better than standard cable?

Better shielding translates to better hum-rejection, and less interference.

How can I avoid interference?

Avoid running audio and power cables together. If possible, isolate power sources from audio connections. Use balanced cables whenever possible.

Do I lose signal integrity with length of cable?

Unbalanced cables gain hum with length. The impedance of the equipment also contributes to signal integrity. Hum-pickup and high-frequency loss can result from using long cables with high-impedance equipment.

What’s the advantage in using a snake?

A SNAKE or MULTICORE AUDIO CABLE is a group of shielded cables encased together for efficiency and uniformity. There is one large cable to run, versus several individual cables of varying lengths and qualities.

What is a ground loop?

Annoying hum in your signal chain is characteristic of a ground loop. A ground loop results when a piece of gear has more than one ground connection. This can happen when you run audio cables between two pieces of equipment, because both pieces of gear are grounded through their AC cables, so the shield in the connecting audio cable serves to complete a ground circuit loop.

How can I avoid ground loops?

Using a transformer between grounded pieces of gear breaks the loop. A direct box can have this effect, or you can use a 1:1 isolation transformer.. Another option is to use only one circuit breaker in your power connection (so make sure your outlets/power sources are wired to one breaker).