When the picture, as a visual, is finally cut the way the director wants it, and all the sound effects, dialog and music have been separately mixed (balanced) and finalized ("built"), they are all brought together to be merged at 'the dub' at a 'dubbing stage' - usually a studio facility which looks like a combination movie theater and a recording studio engineering room (projectors, screen, theater seats, a huge electronic mixing board, etc.). In a sense, it's kind of like an experimental kitchen... a search for just the right brew of ingredients which will result in the best filmic presentation. This kitchen, though, has many cooks: The sound effects people, the dialog people, the music people, the director, the dubbing mixers, the producer(s), and so forth. It is very much, then, a kind of creative fisticuffs where all "contenders" vie for attention and lobby for their point of view. Depending on a host of factors, not the least of which is each director's individual conception of his film, sometimes music wins and sometimes it loses. When music "loses" (let's say , dialed down and off into the background somewhere or excised here and there altogether) its not usually a "bad mix", but a result of a series of creative choices thought necessary to advance the filmic work taken as a whole.
