Music producers are geeks and provide knob twiddling.
Granted, my response doesn't quite capture the complex roles of either film producer or music producer. Shit, I could be completely wrong, for all I know. But it sounded good at the time. Due in no small part to his reputation, as well as the interviews I've read, I've always pictured him sitting behind a recording console, muttering obscenities to himself, encouraging bands to their faces and dissing them behind their backs. Great take, Gavin.