Brian Eno on Generative Art
Part I

"One of my long-term interests has been the invention of 'machines' and 'systems' that could produce musical and visual experiences. Most often these 'machines' were more conceptual than physical: the point of them was to make music with materials and processes I specified, but in combinations and interactions that I did not.
My first released piece of this kind was 'Discreet Music' (1975), in which two simple melodic cycles of different durations separately repeat and are allowed to overlay each other arbitrarily. (Thus, for instance, if one cycle is 29 seconds long and the other is 33 seconds long, they will come back into sync every 957 (i.e. 29 * 33) seconds. Subsequently I released 'Music For Airports', 'On Land', 'Thursday Afternoon', 'Neroli' and other works, all of which use variations on this and similar 'automatic' systems.
In my audio-visual installations I found another way of making ever-changing music. I distributed the pre-recorded musical elements over several (usually four to eight) audio cassettes of different lengths. These were all played back simultaneously, each cassette feeding its own amplifier and pair of speakers. It was thus possible to make music that was different at any point in space and time- or effectively so, because in fact the cassettes would have come into sync again after a few years, if any of the shows had lasted that long (e.g. five cassettes of lengths 23,25.5, 30.2, 19.7 and 21.3 minutes would fall into sync about every 14 years).
I enjoyed these shows- especially the knowledge that the music I was hearing at any given moment was unique, and would probably never be heard in exactly that way again."

From "A Year With Swollen Appendices", page 330