Editing Variable-gain amplifier (section)

== In sound mixing consoles ==

Some [[mixing console]]s come equipped with VCAs in each channel for [[console automation]]. The [[Fade (audio engineering)|fader]], which traditionally controls the audio signal directly, becomes a DC control voltage for the VCA.  The maximum voltage available to a fader can be controlled by one or more master faders called '''VCA groups'''.  The VCA master fader then controls the overall level of all of the channels assigned to it.<ref>{{cite web |title=Allen & Heath ML3000 Block Diagram |url=http://www.allen-heath.com/media/ML3000-Block-Diagram.pdf|archive-url=https://web.archive.org/web/20221014092711/http://www.allen-heath.com/media/ML3000-Block-Diagram.pdf |archive-date=2022-10-14 }}</ref>  Typically VCA groups are used to control various parts of the mix; [[Vocal music|vocals]], [[guitar]]s, [[drum]]s or [[Percussion instrument|percussion]].  The VCA master fader allows a portion of a mix to be raised or lowered without affecting the blend of the instruments in that part of the mix.

A benefit of VCA sub-group is that since it is directly affecting the gain level of each channel, changes to a VCA sub-group level affect not only the channel level but also all of the levels sent to any post-fader mixes.  With traditional audio sub-groups, the sub-group master fader only affects the level going into the main mix and does not affect the level going into the post-fader mixes.  Consider the case of an [[Musical instrument|instrument]] feeding a sub-group and a post-fader mix.  If you completely lower the sub-group master fader, you would no longer hear the instrument itself, but you would still hear it as part of the post-fader mix, perhaps a [[Reverberation|reverb]] or [[chorus effect]].<ref>{{cite web |url=http://www.allen-heath.com/media/ML3000-USER-GUIDE.pdf |title=Allen & Heath ML3000 User Guide}}</ref>

VCA mixers are known to last longer than non-VCA mixers.  Because the VCA controls the audio level instead of the physical fader, decay of the fader mechanism over time does not cause a degradation in audio quality.

VCAs were invented by [[David E. Blackmer]], the founder of [[dbx (company)|dbx]], who used them to make [[Dynamic range compression|dynamic range compressor]]s. The first console using VCAs was the Allison Research computer-automated recording system designed by [[Paul C. Buff]] in 1973.<ref>{{cite book |author=Richard James Burgess |title=The History of Music Production |page=134 |url=https://books.google.com/books?id=8J6zAwAAQBAJ&pg=PT134 |date=2014 |publisher=Oxford University Press |isbn=9780199385010}}</ref> Another early VCA capability on a sound mixer was the series of [[Music Center Incorporated|MCI]] JH500 studio recording desks introduced in 1975.<ref>{{cite book |last=Self |first=Douglas |title=Audio Engineering Explained |date=2012 |page=249 |publisher=Taylor & Francis |isbn=9781136121258 }}</ref> The first VCA mixer for live sound was the PM3000 introduced by [[Yamaha Pro Audio|Yamaha]] in 1985.