Interactive Music Systems
We tend to think interactive music started with video games like Frogger, but Mozart held public concerts where musicians would play a score arranged by audience participation of throwing dice (“Musikalsches Würfelspiel”). What was true then is also true now: people enjoy influencing how music is played, or interacting with proxies that cause changes in music. Interactive music is often employed to reduce listener fatigue, because people tend to spend more time in a given play pattern than listening to the same music cue in linear media.
Horizontal Sequencing: using crossfades to switch between two different streams, or rearranging the order in which different musical “chunks” are presented.
Vertical Layering: Additive, where one, some or all layers can play simultaneously and everything still works; or Interchange, where some layers are mutually exclusive.
Music Data: Individual notes/samples are available to play and a separate instruction stream (a la player piano roll) sequences how to play them. Examples include MIDI and MOD.
Generative Music, also known as Algorithmic Composition
Some random element is introduced to support indeterminancy, like rolling dice. Rules govern how likely different musical events may happen. Wind chimes are a kind of generative music system.
As powerful and compelling as these interactive music forms are, linear music continues to play an important role, often being the best solution for a given situation in a video game.