Editing Balanced line (section)

{{short description|Electrical circuit with two conductors of equal impedance}}
{{Redirect|Balanced|other uses|Balance (disambiguation)}}
{{Use British English|date=June 2023}}

[[File:Noise rejection on balanced line.svg|thumb|upright=1.5|A signal transmitted over a balanced line. The signal is kept intact while the noise (which appears as a [[common-mode signal]] at the receiving end) is rejected perfectly.]]

In [[telecommunications]] and [[professional audio]], a '''balanced line''' or '''balanced signal pair''' is an [[electrical circuit]] consisting of two [[Electrical conductor|conductors]] of the same type, both of which have equal [[electrical impedance|impedances]] along their lengths, to [[ground (electricity)|ground]], and to other circuits.<ref>Young EC, ''The Penguin Dictionary of Electronics'', 1988, {{ISBN|0-14-051187-3}}</ref> The primary advantage of the balanced line format is good rejection of [[Common-mode signal|common-mode noise]] and [[Interference (communication)|interference]] when fed to a [[Differential signalling|differential]] device such as a [[transformer]] or [[differential amplifier]].<ref name="AES">G. Ballou, ''Handbook for Sound Engineers'', Fifth Edition, Taylor & Francis, 2015, p. 1267–1268.</ref>

As prevalent in [[sound recording]] and reproduction, balanced lines are referred to as [[balanced audio]].

A common form of balanced line is [[twin-lead]], used for radio frequency communications. Also common is [[twisted pair]], used for traditional telephone, professional audio, or for data communications. They are to be contrasted to [[unbalanced line]]s, such as [[coaxial cable]], which is designed to have its return conductor connected to [[ground (electricity)|ground]], or circuits whose return conductor actually is ground (see [[earth-return telegraph]]). [[Balanced circuit|Balanced]] and [[unbalanced circuit]]s can be interfaced using a device called a [[balun]].

Circuits driving balanced lines must themselves be balanced to maintain the benefits of balance. This may be achieved by transformer coupling ([[repeating coil]]s) or by merely balancing the impedance in each conductor.

Lines carrying symmetric signals (those with equal amplitudes but opposite polarities on each leg) are often incorrectly referred to as "balanced", but this is actually [[differential signalling]]. Balanced lines and differential signalling are often used together, but they are not the same thing. Differential signalling does not make a line balanced, nor does noise rejection in balanced cables require differential signalling.