Generative music is a term popularized by Brian Eno to describe music that is ever-different and changing, and that is created by a system.
In 1995 whilst working with SSEYO's Koan software (built by Tim Cole and Pete Cole who later evolved it to Noatikl then Wotja), Brian Eno used the term "generative music" to describe any music that is ever-different and changing, created by a system. The term has since gone on to be used to refer to a wide range of music, from entirely random music mixes created by multiple simultaneous CD playback, through to live rule-based computer composition.
Koan was SSEYO's first real-time music generation system, developed for the Windows platform. Work on Koan was started in 1990, and the software was first released to the public in 1994. In 1995 Brian Eno started working with SSEYO's Koan Pro software, work which led to the 1996 publication of his title 'Generative Music 1 with SSEYO Koan Software'.
Eno's early relationship with SSEYO Koan and Intermorphic co-founder Tim Cole was captured and published in his 1995 diary A Year with Swollen Appendices.
There are four primary perspectives on generative music (Wooller, R. et al., 2005) (reproduced with permission):
Music composed from analytic theories that are so explicit as to be able to generate structurally coherent material (Loy and Abbott 1985; Cope 1991). This perspective has its roots in the generative grammars of language (Chomsky 1956) and music (Lerdahl and Jackendoff 1983), which generate material with a recursive tree structure.
Music generated by a system component that has no discernible musical inputs. That is, "not transformational" (Rowe 1991; Lippe 1997:34; Winkler 1998). The Wotja software by Intermorphic, and the Koan software by SSEYO used by Brian Eno to create Generative Music 1, are both examples of this approach.
Music generated by processes that are designed and/or initiated by the composer. Steve Reich's It's Gonna Rain and Terry Riley's In C are examples of this (Eno 1996).
Non-deterministic music (Biles 2002), or music that cannot be repeated, for example, ordinary wind chimes (Dorin 2001). This perspective comes from the broader generative art movement. This revolves around the idea that music, or sounds may be "generated" by a musician "farming" parameters within an ecology, such that the ecology will perpetually produce different variation based on the parameters and algorithms used. An example of this technique is Joseph Nechvatal's Viral symphOny: a collaborative electronic noise music symphony created between the years 2006 and 2008 using custom artificial life software based on a viral model.