One of Steve Reich's early experiments in "process music". Four microphones are hung on their cables above four loudspeakers to which they are connected. When the microphones are directly above the speakers, a feedback tone is produced. Four 'performers' set the microphones swinging back and forth and step back out of the action. Each microphone/speaker circuit emits a series of short whoops of feedback as the microphone passes over the speaker. With slightly different periods of swing, the four microphones slowly get out of synch with each other. Eventually they all come to rest and emit a constant tone each. The piece is then brought to an end.
The four swinging performers are John Coulter, John Kim, Clovis McEvoy and Irazema Vera.