[gmueckl]

Background music in games has had weird dynamic elements for decades. Lucas Arts adventures that used iMUSE occasionally had variants of tracks that they would blend between. Early versions that relied on MIDI hardware could also incorporate tempo changes anywhere in the track in sync with the on screen transitions. The graveyard in Monkey Island 2 is a good example: it has one track that shifts its mood slightly between screens.

A more generative example is the music in Portal 2. There are several aspects to its music that are subtle, purely generative and integrated with the gameplay. For example, the each receiver for the laser beams start playing an additional, random voice over the background music track as long as it is hit by a ray. It is a bit faint, bit it is there. It becomes cool in those levels where you have several of them next to each other They are starting to play a randomized concert while you are solving the puzzle. Someome made a long and elaborate writeup about this and other aspects of the game's music, but I can find it now.

It is a but funny because games shifted away from using sound synthesis amd sampling for music to studio recorded tracks over time as they started to have enough storage space for it. But this now limits how you can process the music to make it dynamic.