About Balanced Audio Signals

Audio cables can be either balanced or unbalanced, depending on their intended use. For long cable runs, especially when using relatively low microphone levels, a three-wire balanced audio circuit reduces noise. Balanced audio cables use the principle of phase cancelation to eliminate noise while maintaining the original audio signal.

A balanced audio cable sends the same audio signal on two wires, but inverts the phase of one signal by 180 degrees.

Figure. Illustrations showing an original signal and the same signal inverted.

When noise is introduced into the cable, it is introduced equally to both the original and the inverted signal.

Figure. Illustration showing the effects of noise on original and inverted signals.

When the signal arrives at its destination, the inverted signal is put back in phase and both signals are combined. This puts the original and inverted signals back in phase, but it causes the noise signals on each line to be out of phase.

Figure. Illustration showing signals with noise, in and out of phase.

Now, both audio signals are in phase, but the noise is inverted, causing the noise to be canceled. At the same time, the original signal gets a little stronger because it is sent on two wires and combined. This helps compensate for the reduction in signal strength that occurs naturally on a long cable run.

Figure. Illustration showing the combined signals.

Any noise introduced into the cable across its long run is almost completely eliminated by this process.

Note: Unbalanced cables have no way of eliminating noise and are therefore not as robust for long-distance cable runs, microphone signals, and other professional applications.