Anything on the 2bus is going to respond based on the collective sum of all the routed channels. The 2buss comp on individual stems isn't going to respond the same way as the master mix.
yeah but if its triggered by the collective sum the GR is the same on every stem.
trying to elaborate a bit more detailed what i meant:
lets say we're in pro tools mixing a basic rock song. drums are all bussed to a stereo aux, bass is bussed to a stereo aux, guitars are bussed to a stereo aux and vocals and vocal fx are bussed to a stereo aux.
those stereo auxes represent my stems. all go out to the main mixbus with a comp on it. for example the waves api comp.
on all the auxes i send post fader to bus xy. bus xy is the sidechain input of my api comp.
now the compression going on on the main mix bus will be the same no matter if the compressor reacts to the external sidechain or the internal - cause they are both the same now (equal amount of drums,vocals etc…
.
when i'm done mixing i start to print/bounce stems.
when i print the drums i deactivate all the other auxes outputs - only the drums are send to the mixbus. still the compressor reacts to the sidechain input wich is the "normal" mix so the GR is the same no matter what elements are actually coming out of the mix bus.
same for all the other instruments/stems.
the GR applied to the stems pumps and acts the same on all of the -> the glueing effect from the compression is there when all the printed stems are played back.
this is actually quite usable when mixing on a console. you can print the stems to the daw and be able to do minimal recalls from in the box. vocals up in the bridge bass down a bit in the chorus etc.
still not exactly the same because the harmonic content isn't quite the same but still better than not having no comp on it.
i hope its now a bit clearer what i meant.
i wouldn't do stem mastering though
EDIT: sorry didn't see jeffs post which is basically what i meant
but it would work with the printed mix as well because its basically the same with just the annoying fact the you have to print the mix first