VCA : Voltage Controlled Amplifier
A VCA is a type of routing/grouping device found on larger mixing consoles. It has similarities to a subgroup but when looked at in detail the two are VERY different.
VCA Desks include Allen & Heath ML series. Soundcraft MH Series amongst others.
What do they do?
One of the best documents on VCA's is provided by Allen and Heath and can be found in PDF format. this document explains what a VCA is, and how they are used in a LIVE environment.
Digital mixing consoles often make use of DCA's (Digitally Controlled Amplifiers) these are the same type of device only in the digital domain. the yamaha PM5D is an example of a mixing console using DCA's.
Programming VCA's or DCA's varies from desk to desk. However programming VCA's on an analogue board is usually a simple process. It is unlikely to differ much in process. (selecting VCA programming mode, selecting channels, selecting VCA.)
This process is often activated from the master section of the desk. Mute Groups Are often controlled and programmed from here.