Balanced & Unbalanced Lines

Unbalanced Lines

In this instance, unbalanced doesn't mean faulty or psychologically unstable. Unbalanced lines are used for nearly all domestic audio connections, and also in semi-pro and some pro equipment.
It consists of a send and return path for the audio signal, the return path being an outer screening braid which encloses the send wire and screens it from electromagnetic interference. The screen reduces interference such as hum and RF, but it can't get rid of it completely. Unbalanced lines of over ten metres can suffer from an unacceptable amount of cumulative interference.
Unbalanced lines usually use phono plugs, DIN plugs and standard mono ¼″ jack plugs.

Balanced Lines

Balanced lines are much better at rejecting interference than unbalanced lines.
The cable consists of a pair of conductors enclosed by a screening braid. The send and return paths for the audio signal are provided by the two inner conductors, and the screen doesn't form part of the audio circuit.
Inside the source device, the output signal is split into two opposite phases. These two signals (positive and negative or hot and cold) are fed down the two conductors in the cable. Once the signals reach the receiving device, one of the signal's phase is inverted before it's voltage is added to the other signal. The signals are therefore in phase with each other when their voltages are combined.
Both conductors are affected by interference almost equally, because they are physically so close to each other in the cable. However, when the two identical interference signals reach the receiving device one signal is inverted; the two signals are now out of phase and cancel each other out. The wanted signal is unaffected.

Although balanced lines are effective they can't get rid of all interference, so we still have to keep cables as short as possible and keep them away from mains cables or transformers.
Balanced lines usually use XLR jacks and TRS (stereo) ¼″ jacks.

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