Balanced Audio

The most important function balanced audio performs is to reduce the amount of unwanted noise that has been picked up from audio cables during the sound recording process. Unwanted sound is picked up because the wire picks up all available electronic fields, not just the one that is desired. These extra fields are typically created by the other equipment used in sound recording, particularly other wires. While many wires and cables have high-frequency shielding, this feature is not always effective, and can occasionally contribute to the problem of extra noise. The additional electricity increases the voltage of the wire; this is input into the recording because it is not distinguishable from other sounds. 

Balanced audio cables remove sound interference at the point where they are connected to a mixer. Balanced audio works with two cables. The signals from these cables are designed to cancel each other out.  Each cable carries a different version of the signal being recorded, and they cancel each other out by manipulating the signal balances. The cancellation decreases extraneous noise.
The cables used in balance audio (referred to as balanced cables) consist of a hot line, which carries the sound signal, an earth line, and a cold line. An earth line is actually capable of generating a frequency hum like any other cable. However, there is no need to worry about earth line interference because this line is not part of the audio input. Even if its electrical frequency is picked up by the hot and cold lines, the noise that is generated will be erased later. The hot line has a positive charge and the cold line a negative one. The charge determines which way the signal will flow on each cable; it flows positively on the hot line and negatively on the cold one. 

The signal transmits on the hot and cold lines; the voltage transmitted through the cold line is the inverse of the voltage in the hot line, meaning the signal is upside-down. The sound transmitted on both these lines can pick up extraneous noise, which appears on both cables. This noise is referred to as the common mode signal. This means that each line carries two signals: the inverse signals (desired) and the identical signals (undesired). Once the desired signals meet, which takes place when the cables are attached to the mixer, the signal from the cold line becomes the same as the signal in the hot line; this creates a stronger signal, because now the signals are capable of combining with each other. The reversal of the voltage on the cold line means that the noise it picked up is now inaudible.
When working with balanced audio cables, the standard connector is a 3-pin XLR. This one is used most often because it is extremely durable.  The most widely-used configuration when creating balanced audio with 3-pin XLR is as follows:

•    Pin 1: Shield
•    Pin 2: Hot
•    Pin 3: Cold 

However, there are other connectors that can be used for balancing, including a 2-conductor unbalanced jack with a Tip-Ring Sleeve attached to the device. It is important to check the specs of any device to be used for balanced audio, as they are not created equal. Even some XLR devices will not function when working with balanced audio. It is also important to note that unbalanced and balanced equipments should not be mixed if balanced audio is desired. The unbalanced wires will override the balanced ones, giving an unbalanced sound. This means that if one wants to balanced audio, everything that is used should be balanced, including adapters. This will ensure the quality of the sound.