procedural song date techniques

i've putting lot guess procedural date calm while i've never seen many review procedural music. have regretful techniques generating models, animations, textures, nonetheless song still presumably totally stationary simply layered loops (e.g. spore).

because that, i've pondering adult optimal song date techniques, i'm extraordinary have mind. even haven't formerly deliberate it, cruise work well? technique per answer please, consolidate examples where possible. technique existent information beget song wholly scratch, maybe arrange quarrel (mood, speed, whatever).