Late in 1971 I composed Clapping Music out of a desire to create a piece of music that would need no instruments at all beyond the human body. At first I thought it would be a phase piece, but this turned out to be rather inappropriate since it introduces a difficulty in musical process (phasing) that is out of place with such a simple way of producing sound. The solution was to have one performer remain fixed, repeating the same basic pattern throughout, while the second moves abruptly, after a number of repeats, from unison to one beat ahead, and so on, until he is back in unison with the first performer. The basic difference between these sudden changes and the gradual changes of phase in other pieces is that when phasing one can hear the same pattern moving away from itself with the downbeats of both parts separating further and further apart while the sudden changes here create the sensation of a series of variations of two different patterns with their downbeats coinciding. In Clapping Music it can be difficult to hear that the second performer is in fact always playing the same original pattern as the first performer, though starting in different places.
Clapping Music marks the end of my use of the gradual phase shifting process.
Steve Reich, “Writings about Music”