Clintage -
The groups are a type of mix. (auxes, LR, etc are also mixes)
The matrix is a “mix” of mixes. So you only assign mixes to a matrix. You don’t assign inputs to a matrix.
The DCAs are NOT mixes. They are like remote controls for any slider controlling an input or a mix. (although it does not move the slider)
There are lots of different scenarios. Here are some scenarios where you might want want to use a DCA.
Suppose you submix your inputs to groups (say drums group, vocal group, instrument group). Then you assign those 3 groups to LR main mix. You plan on running three sets of speakers: main speakers, front fills, and outfills. So to do this you create three matrices all fed from LR. 1 matrix for mains, 1 for front fills and 1 for outfills. You can set the levels for each set of speakers to your liking.
So your signal routing looks like this:
inputs → groups → LR → Matricies
Suppose your are doing a board recording based from the LR mix also. So it now looks like this:
inputs → groups → LR → (Recording and Matricies)
Lets see now where a DCA would work well:
LR feeds your output level to the speakers and it also feeds the recording level.
So LR works as a master volume for your entire mix. So if you want to make the live volume louder or softer, you could grab the LR slider, but that would affect the recording and make the level change. Or, you could grab the matrix sliders but then
you have to grab 3 sliders. So the issue here is that we do not have a MASTER volume that affects only the overall speaker output.
You can use 1 single DCA to essentially control the 3 matrix outputs yielding you a MASTER volume control that preserves your relative levels matrix levels controlling main speakers, front fills and outfills. AND it would s not affect the recording level. The LR fader can stay put the whole night.
So what you would do is make a DCA to that controls the 3 matrix outputs. So you have one single MASTER slider that controls that live volume that does not affect the recording level. Its almost like turning the amps down instead of riding LR all night.
Another example would be controlling specific inputs.
Consider controlling all microphone inputs (exclude anything that is direct input because it does not feed back) . You might assign all microphone inputs to be controlled by a dca. In case you get feedback, you can quickly reduce the input channels that are mics and leave the direct inputs unaffected. WHen you find the cause of feedback, you can turn the dca back up.