Editing Dynamic range compression (section)

== Side-chaining ==
[[File:Compressor Sidechain.svg|thumb|300px|The sidechain of a feed-forward compressor]]
{{listen | filename = Uplifting Trance Sidechain.ogg| title = Uplifting Trance Sidechain| description = The first 8 bars are without side-chaining applied, the second 8 are with side-chaining. | format = [[Ogg]]}}

A compressor with a side-chain input controls gain from main input to output based on the level of the signal at the side-chain input.<ref name="Colletti">{{Cite web |url=http://www.sonicscoop.com/2013/06/27/beyond-the-basics-sidechain-compression/ |title=Beyond The Basics: Sidechain Compression |last=Colletti |first=Justin |date=2013-06-27 |website=SonicScoop |access-date=2015-03-16}}</ref> An early innovator of side-chain compression in an effects unit was the [[Eventide, Inc|Eventide]] Omnipressor from 1974.<ref>{{cite web |title=50th Flashback #3: The Omnipressor |url=https://www.eventideaudio.com/blog/aagnello/50th-flashback-3-omnipressor |website=Eventide Audio |date=10 March 2021 |access-date=17 May 2021}}</ref> With side-chaining, the compressor behaves in the conventional manner when both main and side-chain inputs are supplied with the same signal.

The side-chain input is used by [[disc jockey]]s for [[ducking]] – lowering the music volume automatically when speaking. The DJ's microphone signal is routed to the side-chain input so that whenever the DJ speaks the compressor reduces the volume of the music.

A sidechain with [[equalization (audio)|equalization]] controls can be used to reduce the volume of signals that have a strong spectral content within a certain frequency range: it can act as a [[de-esser]], reducing the level of vocal [[sibilance]] in the range of 6–9&nbsp;kHz.<ref>{{Cite magazine |last=Senior |first=Mike |date=May 2009 |title=Techniques For Vocal De-essing |url=http://www.soundonsound.com/sos/may09/articles/deessing.htm |department=Sound Advice |magazine=Sound on Sound |access-date=2015-03-16}}</ref> Another use of the side-chain in music production serves to maintain a loud bass track without the [[bass drum]] causing undue peaks that result in loss of overall [[Headroom (audio signal processing)|headroom]].<ref name="Colletti" />