In it’s simplest definition, balanced audio just means to transfer an audio signal through a cable without picking up any unwanted electrical hum. This hum can come from a wide variety of sources, and is usually picked up from other electrical equipment around the stage or studio.
Balanced cables were developed to help negate the pickup of this unwanted electricity. These are in contrast to unbalanced cables, such as a regular guitar cable, and are typically seen in the form of an XLR microphone cable or a TRS Cable.
An unbalanced cable consists of two wires – one to transmit an audio signal (conductor) and another to act as a ground. A balance cable adds a third wire to offer a second conductor that transmits an inverted form of the original signal. Some diagrams may make this more clear.
This is a depiction of a signal. which is made of troughs and peaks that repeat in a cycle.
Now the inverted signal – carried on the second conductor wire, does the opposite of the original signal, but at the same time:
If these signals are combined together, they would cancel each other out leaving no signal at all:
This is exactly what happens in a balanced audio cable, except it’s the unwanted noise that gets canceled out. In the following diagram, the red line represents unwanted noise carried on the two conductor wires:
Why, then, doesn’t the original audio signal get canceled out as well? When the balanced signal reaches its destination – the balanced jack – the inverted signal becomes reverted to match the original signal. What’s left is the cancellation of unwanted noise while the original signal is maintained.