thats what ive always thought they did, or they would set it up to bring in multiple stems (or whatever) and then a controller to control filters and shit i could be way off though How I believe it works as he can bring in stems and control their levels, as well as tweak each stem (to a degree) by having certain fx and stuff he can trigger, which is all set up beforehand in ableton, ready to trigger.. Also has a pad to apply extra loops and one hit samples