What is a balanced connection? | Basic Pro Audio Concepts

THE GIST

Balancing is a method of transmitting audio over medium-to-long distances with minimal electromagnetic interference. This is accomplished by sending an out-of-phase copy of a signal along with the original through the same cable, then reversing the out-of-phase copy and combining the two. Any noise or interference picked up along the way is cancelled out, leaving the original signal pure.

Purpose

The copper wires that carry audio signals are sensitive to interference from electromagnetic fields, meaning they can pick up unwanted noises on their way from point A to point B. These noises can come from electrical wiring, radio frequencies, and even other pieces of audio equipment.

A braided wire or foil shield is often used to absorb this interference and send it to ground, but it’s not a foolproof technique. The chance for interference becomes greater with long cable runs, like stage snakes and microphone cables, creating the need for a better solution.

Theory

A balanced connection requires a specially designed input, output, and the cable connecting them all working in tandem. The output of the first device consists of one pin sending the normal signal (positive or “hot”), a polarity-reversed copy (negative or “cold”), and an extra pin connected to ground.

As the audio travels down the cable, any noise picked up along the way is picked up equally on both wires. At the input of the second device, the negative signal is flipped back to positive polarity, and the signals are combined. The noise present in each signal is now 180 degrees out of phase and cancels itself out, leaving the original signal pure.

Cables for Balanced Connections

Although balancing is a property of the equipment involved and not the cable, cables used for balanced connections are almost always of the twisted pair, shielded type.

Two conductors are twisted together to ensure noise is picked up equally on both sides (as well as to help with the overall stability of the cable) and each is insulated with PVC tubing. A braided copper or foil shield is wrapped around the pair as the first layer of defense, rejecting or absorbing most of the interference and sending it harmlessly to ground.

Cables used in balanced connections can have different types of connectors but always feature two contacts per channel of audio and usually a ground contact. XLR is used for microphone cables, SpeakOn is used for locking speaker connections, and Tip-Ring-Sleeve (TRS) connectors (which look like a guitar cable with one extra metal contact) come in quarter-inch, eighth-inch, and Tiny Telephone (patch cable) sizes.

Balanced connections are also featured on multichannel D-sub connectors, where a single ground shields all channels.

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