Reich and Pythagoras

In many of his compositions, Steve Reich employs the following rhythm of eight notes, which repeats over a twelve-unit span. The colors are my own, intended to facilitate the reader’s orientation: the white dots indicate the absence of onsets.

Music researchers have proposed several features that set this rhythm apart from other rhythms; some are summarized in Gottfried Toussaint’s recent book The Geometry of Musical Rhythm (CRC Press, 2013), along with the author’s own ideas. I propose another such feature.

On the one hand, this figure is the well-known smallest-integer illustration of the Pythagorean Theorem. On the other hand, and admittedly rather incidental to Pythagoras, each of the three squares is a metrical interpretation of some segment of the repeating Reich rhythm. The side of a square shared with the triangle serves as the “left” side of the square’s “score”: the rhythm is then read as usual, first left to right, then top to bottom. Each square represents a “pure” meter: a triple of triples (like three measures of 3/8), a quadruple of quadruples (like four measures of 4/8), and a quintuple of quintuples (like five measures of 5/8). The first two are quite easy to experience; however, the last takes a little practice, but is possible.

The triangle in the middle is completely lined with dots. This means that, in each of the three metrical interpretations, there is an onset on every downbeat. No rhythm besides Reich's (up to rotation) with eight or fewer onsets in the same repeating span has this property. While there exist other eight-onset rhythms over longer repeating spans that have this property, only Reich's rhythm among these has this property plus the equivalent for sextuples; that is, all downbeats for a "pure" sextuple meter.