All mixing consoles have grouping facilities. It is the very heart and soul of mixing. It means that several individual channels are grouped together and mixed into one output.
You can subgroup too - you can mix several channels into one subgroup, and then mix more channels with that subgroup into the main outputs, perhaps taking in other supgroups too.
To give one example of what this is good for, imagine a mix that includes a drum set. The mix is perfect. Now the producer asks for the drums to be louder.
Oh dear - you have to raise the levels of all of the faders covering the drum set, all by exactly the same amount. And then the producer says he isn't happy and he wants them put back again.
This would be an even bigger problem in live sound where it is more likely you would want to change levels, and perhaps more often.
So you route the faders for all of the drums to a pair of subgroups (a pair for stereo), then you route these subgroups to the mix, along with all the other channels.
Now you can control the level of the drums with just two faders.
But the limitation of this kind of subgrouping is that you have to mix the signals. What if you wanted to control the levels of certain channels simultaneously, as in the example, but you didn't want to mix them? That is probably less likely with the drum set, but there are many situations where you want to route signals to different outputs without mixing them, particularly in live and theater sound.
This is where VCA subgrouping comes in. Here, the level of the signal in each channel is controlled by a voltage controlled amplifier, or VCA. The fader controls the VCA and the VCA controls the signal level.
But the VCA can also control the signal level from a voltage input. This source of voltage comes from a VCA master fader. Consoles with VCA grouping commonly have eight VCA master faders.
Now, a number of channels can be selected to one VCA master fader, and this one VCA master fader will control the levels of all of those channels, in proportion to the levels already set on their individual faders.
All of this without mixing the signals!
Oddly enough, digital mixing consoles do this as standard. Create a group of faders and operate one of them as their master - they will all go up and down in level. And you don't have mix the signals if you don't want to.
But the concept of VCA grouping remains, and it is a good one. Thumbs up to the unknown audio hero who invented it!
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