For his 1965 composition “It's Gonna Rain”, Steve Reich designed a generative mechanical system.

Steve Reich: It's Gonna Rain (1965)

It was a system of two tape recorders.

A system of two tape recorders

Reich had made field recordings of speech on tape.

With recorded speech

He made two short identical loops from his recordings. One for each tape recorder.

Two identical loops

The tape recorders were set to slightly different speeds.

One would play a little faster than the other.

With slightly different speeds

This started a phasing process. A continuously changing soundscape was generated from the short loops.

A generative phasing process