So far in our What’s the Difference series, we’ve considered AFL/PFL and Pre-Fade/Post Fade. Today, we’re going to look at another pairing that I see confused all the time. That is the difference between Groups and VCAs.
A Group is a Mix Bus
A group is a place to send channels post-fader. To make this clearer, the LR main output on your console is technically a group. So is the Mono output if your mixer has one. When you send a channel to a group, it is after all processing and the fader, so it is truly the final step on the way out of the console. You can assign channels to as many groups as you want; up to the number of groups you have. The level of the channel going to the groups will always be the same. In this way, groups are different from auxes. With an aux, each aux send goes out at its own level. Sending a channel to two groups sends the same exact signal to both groups.
A VCA is a Remote Control
A VCA (short for Voltage Controlled Amplifier) is really a way to remotely control the level of a channel or group of channels from a single fader. When you assign a channel to a VCA, you can add and subtract gain from that channel using the VCA fader and/or the channel fader. Moving the VCA master up by 5 dB will have the same effect on the channel as moving the channel fader up 5 dB. Turning off the VCA master will effectively mute the channel(s), making it easy to turn entire groups of channels on and off with one fader move.
When to Use Them
I wrote a much longer series on this topic some time back, but here’s the shortened version. Groups are useful for applying the same processing to a group of inputs. Clever, huh? For example, if you want to do some parallel compression on the drums, you can assign all the drum inputs to a group and insert a compressor on the group. Mix that with the uncompressed version and you have parallel compression. Or perhaps you want to subtly compress all the BGVs. Same thing. Only don’t assign them to the main LR bus; send them to the group, compress then send the group to the LR mix.
VCAs are useful for mixing similar types of instruments. On digital consoles, you may not have the faders on the surface for all your inputs. Really large analog consoles may be a long reach. So, you can combine channels into one to make it easier to manage. For example, you may set up the mix for the drum kit, then assign all the drum channels to a VCA. Because the drums are one instrument, you can adjust the level of the drums with the VCA. Some engineers like to put the bass and kick on a VCA and move their level together. Others will assign all the keys to a VCA and all the guitars to another.
It’s important to note that a VCA is not better than a group, nor is a group better than a VCA. They are different. Not all mixers—especially small ones—have VCAs so you have to make do with groups. But when you have both, use them for what they are good at.
VCAs and DCAs
On some digital consoles, Yamaha for example, VCAs are called DCAs. DCA stands for Digitally Controlled Amplifier. The function is the same, but the underlying technology is different. For all practical purposes, they are the same.
This is a pretty simplified explanation. For a lot more detail, check out some of the posts below.
Other posts with more detail: