A VCA, or Voltage Controlled Amplifier, is an amplifier that varies its gain depending on a control voltage. In a mixer this applies to signal routing and channel strips.
The purpose of a VCA is to allow you to turn up or down a group of faders while maintaining the relative levels throughout the group. There is no signal processing in a VCA, just overall volume control. The VCA group level affects not only the channel’s level, but also all of the levels sent to any post fader mixes
(844 VCA courtesy of www.modulargrid.net)
As used in Master Fader, there is no literal ‘Voltage’ Control, as it’s all controlled via digitally, but the term is still applied as an homage to the VCAs and great analog consoles of yore.
A VCA is like a Subgroup in that they both may be used as master faders for a group of channels on their way to the main mix. The main difference is that Subgroups have basic output DSP and VCAs do not.
The differences between the input channel strips and VCA channel strips in Master Fader are:
No Source Select — There is no digital trim on VCAs, so it will be absent from the routing view for these channel strips. However, routing may still be accessed in order to assign channels to VCAs and route them to view groups.
No EQ — VCA channels do not have EQ, so there is no EQ button.
No Dynamics — VCA channels do not have compressors or gates, so there is no dynamics button. No Pan Slider — VCA channels do not have pan sliders.
No Channel Assignments — VCA channels do not have channel assignment indicators.
No Meters — VCA channels do not have meters.
(Channels assigned or “routed” to a VCA in Master Fader)