Think of the DCA as a remote control for a group of faders. When you lower the DCA it effectively lowers all of the faders in that are assigned by the same amount, keeping their relation to each other in tact. If you assigned all of your drum faders, you can turn up or down the entire drum mix without actually changing the mix between individual drums. The drum faders themselves would not actually move, but they would be raised or lowered according to the position of the DCA fader. The mute on that DCA will also mute all of the faders assigned.
DCAs can control any faders (input, output, FX sends, FX returns, etc) and are not an audio path like a subgroup. You can’t put additional processing on a DCA (like compressors or EQ) like you could with a subgroup.
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