Editing Balanced audio (section)

== Interference reduction ==

Balanced audio connections use a number of techniques to reduce noise. 

A typical balanced cable contains two identical wires, which are twisted together and then wrapped with a third conductor (foil or braid) that acts as a [[Shielded cable|shield]]. The two wires form a circuit that can carry an [[audio signal]].

The term ''balanced'' comes from the method of ''balancing'' the [[electrical impedance|impedance]] of each wire in the circuit; the line and all circuits directly connected to it (such as the driver and receiver) must have identical impedances with respect to some reference point. This means that much of the electromagnetic interference will induce an equal noise voltage in each wire. Since the differential device at the receiving end only responds to the [[subtraction|difference]] in voltage between the two signal lines, noise that is identical on both wires is rejected. This method can be implemented with a [[differential amplifier]]. A [[transformer]] may also be used instead of an active input stage.

A [[twisted pair]] makes the loop area between the conductors as small as possible, and ensures that a magnetic field that passes equally through adjacent loops will induce equal levels of noise on both lines, which is canceled out by the differential device in the receiver. If the noise source is extremely close to the cable, then it is possible it will be induced on one of the lines more than the other, and it will not be canceled as well, but canceling will still occur to the extent of the amount of noise that is equal on both lines.

The separate shield that is commonly provided in a balanced audio cable also yields a [[noise rejection]] advantage over an unbalanced two-conductor arrangement (such as used in typical home stereos) where the shield must also act as the signal return wire. Therefore, any noise currents induced into a balanced audio shield will not be directly modulated onto the signal, whereas in a two-conductor system they will be. This also prevents [[ground loop (electricity)|ground loop]] problems, by separating the shield/chassis from signal ground.