Steve Reich calls Pendulum Music the "ultimate process music." Microphones are suspended from the ceiling and swing past speakers, generating feedback. Keith Potter, in Four Musical Minimalists, describes how Reich originated the piece with the artist William Wiley (and his student Bruce Nauman) when they were were in New Mexico. The idea came when they accidentally put a microphone in front of the speaker. When incorporated in an overall multi-media event Over Evident Falls, the piece was played in black light. Very much in the spirt of the sixties and "consciousness revolution."
And for some reason, Ensemble Avant Garde records it three times on their CD .