Pro Tools: Using VCAs

VCA stands for Voltage Controlled Amplifier, a technology used in some analogue live mixers to allow you to control the levels of multiple channels at once.

What can a technology from analogue consoles bring to your Pro Tools workflow?

VCA Master tracks are available in Pro Tools Studio and Ultimate, but not Artist or Intro. They provide a convenient way to govern the level of multiple tracks from a single fader. But there are other ways to control the level of multiple tracks, so what makes VCAs different and when are they useful?

I first encountered VCAs on a large‑format Midas live console in the late 1990s. I understood subgroups, but a bank of apparently subgroup‑like faders labelled VCA left me wondering where they sat in the signal path.

Anyone familiar with VCAs will recognise the mistake in that question. A subgroup receives audio from several source channels via an internal bus, where it sums those signals together and provides a single fader to control their combined output. By contrast, a VCA has no audio input or output. It is a remote fader for a collection of source tracks, controlled independently of their routing through the mixer by these VCA faders.

That raises questions: why use a control that carries no audio? Doesn’t Pro Tools already provide something similar with Mix Groups, and what does a VCA add to the other ways of controlling multiple tracks from a single fader?

...a VCA has no audio input or output. It is a remote fader for a collection of source tracks.

Bus Routes

Submixing can be achieved with either an Auxiliary Input or a Routing Folder. In both cases, several source tracks are routed to a common bus, where their signals are summed, and their combined level controlled from a single fader. This also provides shared inserts for bus processing and straightforward metering of the combined signal.

The other contender for controlling the level of multiple tracks is the Mix Group. These have been available in Pro Tools for a long time, and by linking controls across member tracks they can considerably streamline the management of large sessions.

Mix Groups are different in approach from submixes, because the control is independent of audio routing. When volume is linked within a Mix Group, moving the fader of one grouped member track causes the other member tracks’ faders to move relative to it. The offsets between their levels are maintained, preserving their internal balance, but this is achieved by controlling the member tracks’ faders rather than by boosting or attenuating their summed output.

VCA...