Balanced and Un-Balanced Audio

What is Un-Balanced Audio?

Un-balanced audio is what is found in typical home stereo.

An unbalanced line uses one wire for the signal and another for the ground. Unlike balanced lines, unbalanced lines use the ground for signal return. In typical unbalanced cables, the ground is the cable shield.

Traditional unbalanced cables that we see, uses two lines to transmit the audio signal- a hot line i.e. which carries the signal and the earth line. So this is all that is required to transmit the audio and is common in short cables ( where noise is less of a problem).

Unbalanced work best allowing an audio signal to pass from one piece of equipment to the next with minimal interference. However, they have the drawback of picking up undesirable noise and hum.

What is Balanced Audio?

Balance audio is a method of minimizing unwanted noise from interference in audio cables. The idea is that any interference picked up in a balanced cable is eliminated at the point where the cable plugs into a Sound Mixer or other equipment.

Balance audio uses the method of interconnecting audio equipment using impedance balanced lines. Balanced Audio uses a cable made up of two conductors that are twisted together and surrounded by an overall shield. The basic idea being that each conductor is connected to impedance at each end of the line. The audio on the two conductors is exactly the same, except that one of the conductors has the audio inverted at the source piece of equipment. The input of the destination equipment inverts the Inverted audio and sums the two channels together.

Balanced audio cables use an extra line, and consist of a hot(positive), cold line (negative) and earth.

The audio signal is transmitted on both the hot and cold lines, but the voltage in the cold line is inverted (i.e. the polarity is changed) so it is negative when the hot signal is positive. These two signals are often referred to as being 180 degrees out of phase with each other but this is technically incorrect – the signals are not actually out of phase, they are opposite polarities, i.e. one signal is effectively flipped upside down rather being delayed 180 degrees.

When the cable is plugged into an input equipment, the Hot and Cold signals are combined. Normally one would expect these two signals to cancel each other out, but at the input stage the inversion is reversed before being merged together, so they actually combine to form a stronger signal.