Editing Balanced line (section)

== Balanced and differential ==
{{main|Balanced circuit}}
Many explanations of balanced lines assume symmetric signals (i.e. signals equal in magnitude but of opposite polarity) but this can lead to confusion of the two concepts—signal symmetry and balanced lines are quite independent of each other.<ref name="AES"/> Essential in a balanced line is identical impedances in the two conductors in the driver, line and receiver (impedance balancing). These conditions ensure that external noise affects each leg of the line equally and thus appears as a common-mode signal that is rejected by the receiver.<ref name="AES"/> There are balanced drive circuits that have excellent common-mode impedance balancing between the legs but do ''not'' provide symmetric signals.<ref>{{cite web 
 |url=http://www.jands.com.au/support/product-support/audio-technical-materials/geek-files/audio-balancing-issues-explained 
 |title=Audio Balancing Issues 
 |access-date=2014-10-27 
 |author=Graham Blyth 
 |author-link=Graham Blyth 
 |quote=Let’s be clear from the start here: if the source impedance of each of these signals was not identical i.e. balanced, the method would fail completely, the matching of the differential audio signals being irrelevant, though desirable for headroom considerations. 
 |archive-url=https://web.archive.org/web/20161024222509/http://www.jands.com.au/support/product-support/audio-technical-materials/geek-files/audio-balancing-issues-explained 
 |archive-date=2016-10-24 
 |url-status=dead 
 }}</ref><ref>{{cite book
 | title = Sound system equipment
 | edition = Third
 | year = 2000
 | publisher = [[International Electrotechnical Commission]]
 | location = Geneva
 | id = IEC 602689-3:2001
 | pages = 111
 | chapter = Part 3: Amplifiers
 | quote = Only the common-mode impedance balance of the driver, line, and receiver play a role in noise or interference rejection. This noise or interference rejection property is independent of the presence of a desired differential signal.
}}</ref>  Symmetric differential signals concern headroom and are not necessary for interference rejection.<ref>G. Ballou, ''Handbook for Sound Engineers'', Fifth Edition, Taylor & Francis, 2015, p. 1267. “Two signal voltages have symmetry when they have equal magnitudes but opposite polarities. Symmetry of the desired signal has advantages, but they concern head room and crosstalk, not noise or interference rejection.”</ref>