Reich's phasing runs two identical loops at slightly different speeds to generate emergent shifting patterns

Steve Reich, influenced by African drumming and polymetric structures, explored ‘phasing’: playing two identical patterns simultaneously but at slightly different speeds, so they gradually drift out of alignment, creating constantly shifting interference before re-synchronizing. It’s Gonna Rain uses two tape loops slowed against each other; Clapping Music applies the same idea in live performance, with one player repeating while the other steps through rotations at fixed intervals. Phasing is directly implementable in live coding via phase offset and tempo manipulation, and is a paradigmatic case of a simple algorithmic rule generating complex emergent behavior — an ancestor of live coding’s repetition-with-gradual-transformation aesthetic.

Examples

Two near-identical loops at speeds 1 and 1.01 drift into shifting interference before realigning; Clapping Music keeps both at one tempo but rotates one part by one beat at set intervals.

Assessment

Describe phasing in one sentence, explain how it differs from playing two identical loops in sync, and say how it can be realized in a live-coding context.