Should you use them? Which one and why?
VCAs/DCAs and Groups have often confused sound engineers.
Some prefer mixing on one or the other and some use a combination of both. It’s often about preference but there are reasons to use one over the other.
VCAs or DCAs
VCAs/DCAs work like a remote control for the faders assigned to it. You can easily control the input fader level of multiple input channels with one VCA fader. If your kick drum channel fader is at 0 and assigned to VCA 1, moving VCA 1 to + 5 on the VCA will essentially be increasing the level of the kick drum channel at the fader an additional 5dB. When you have all of your drum channels assigned to a VCA you can easily bring the overall drum mix down with one fader preserving the individual mix between the drum channels.
Mix Groups/Sub Groups/Control Groups
Groups are similar, allowing you to group multiple channels together for easier control, but Groups allow you to add processing to those multiple channels whereas VCAs don’t.
Another key difference between VCAs and Groups is that Groups sum all of the signals assigned to them together, they are another gain stage. VCAs do not pass audio.
VCAs will also change the level that the assigned inputs are sending to other buses such Auxes sending to effects. Groups do not.
The biggest benefit to using Groups and or VCAs is efficiency and control. Being able to control and/or process multiple inputs together. If you want to add some compression to your drum mix to make it punch, assign your drums to a stereo group and slap a compressor across the groups.
Using groups and/or VCAs is a great way to handle large channel counts. Considering that most digital consoles have limited faders on the surface, if everything is assigned to Groups/VCAs it’s much easier to mix rather than hunting for channels or flipping through layers and pages. It’s all about control and efficiency….
If you'd like to learn more about VCAs/DCAs/ Groups and mixing, check out the course Mixing Music Live.