Variable-gain Amplifier - in Sound Mixing Consoles

In Sound Mixing Consoles

Some mixing consoles come equipped with VCAs in each channel for console automation. The 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. Typically VCA groups are used to control various parts of the mix; vocals, guitars, drums or 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 to the post fader mixes. Consider the case of an 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 reverb or chorus effect.

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.