Grouping & VCAs

If you’ve been following me for a while, you know that one of my mixing heros is Robert Scovill. A few days ago I ran across one of his writings regarding using subgroups and VCAs when mixing and the place for both. I’ve heard this talk live but its well articulated here and worth a read. Continue on…

“While there are many new and exciting styles of groups coming online with the outbreak of digital live sound consoles, for the purposes of this article, I’m only going to concentrate on two styles: “audio sub groups” and “VCA groups.”

Given that the vast majority of consoles, analog or digital, offer these two styles of groups, I strongly encourage you to thoroughly understand the differences between them and work toward using them.  While many mix engineers tend to use one or the other, they are certainly not mutually exclusive of one another, and when used correctly and together, are a very powerful tool.

Let’s start with audio sub groups. Audio sub groups are generally either mono or stereo and, by definition, provide a summing point for a given number of inputs before they then head off to the left/right master output.  This means that any number of audio inputs can be directed through the audio sub group and the group as a whole can then be moved up or down in volume. By soloing an audio sub group, and listening in headphones, you can then monitor the fader balances of all inputs that are feeding the group, including their pan position.

For example, with the push of the group solo button on a drums group you could listen to the relative blend of all the drum mics and, in turn, affect the overall level of the drum kit in the PA system by moving the group fader without having to change the input fader positions. The input faders would still be feeding any post-fader aux busses even though the audio sub group fader would be at zero.  Additionally, because audio is actually passing through the group, it will usually offer an insert point where you can patch in equalizers or compressors and limiters which, of course, would affect the drum mix as a whole in the PA system.

This is where the difference between audio sub groups and VCA groups comes to light. A Voltage Controlled Amplifier (VCA) does not offer an actual audio path for the inputs assigned to it. Instead, once a number of inputs are assigned to the VCA fader, it essentially works as remote control of the assigned faders.  For example, if you had a blend of eight input faders and you assigned them all to a VCA group, once you move the VCA group fader down, it is exactly as if you simply reached over and pulled the actual input faders down.  The relative levels between the faders would remain the same, but the levels to any post-fader aux buses would now change by how far down in level you moved the VCA master.  VCAs, generally speaking, do not allow you to solo the group unless it is a destructive style “solo in place” because of the lack of audio passing through the group.  Likewise, it does not offer you the ability to insert external processing on the group as a whole.

So, with these concepts now in mind-I’m recommending the following to those of you who have both audio sub groups and VCA groups on your console. Use them both. But use them for different tasks.

Start by using your audio sub groups to assemble the components of your event mix into groups. For example, 1-drums-loops & percussion, 2-bass, 3-keys, 4-guitars, 5-backing vocals, 6-lead vocals, 7-pastor, 8-media.  Once done, then assign these groups to the left/right master output. Try to stay disciplined and keep like inputs in their respective groups.

Say you have a reverb unit dedicated to the drums – assign the reverb return faders to the drums group. This allows you to listen to the actual blend of the drum inputs against the reverb return while soloing the drums audio group.  Likewise, if you mute the drums audio group, you’ll no longer hear the reverb return, even though the drum inputs are still feeding it.

Now all of your VCAs are available for doing what I like to think of as “focused” mixing. Now you can assign VCAs to inputs that you need access to for any given segment of your event. They’re located in one position and available for immediate level manipulation.  Maybe you have a VCA that is simply assigned to only the kick and snare or just the cymbals, maybe even just the toms. Any of these allows you to accentuate a given fill or breakdown in a song with the movement of one single fader.

Or maybe you have the percussion assigned to its own VCA, with those inputs living as a part of the drums audio sub group. It all just depends on what you need to get to at any given time.

This is a wonderful workflow for digital consoles and even some analog consoles, in that you can program the VCA assignments dependent upon what you need to get to at any given time.  It’s all up to your imagination and, if done properly, there is rarely an excuse for missing cues because you were late finding the fader.”