Philip Glass wrote Knee Play 1 for his 1976 opera “Einstein on the Beach.” Glass has said that numbers were sung to help the chorus learn the difficult rhythm patterns. He intended to eventually replace them with other lyrics, but changed his mind.
The guitar and drums play what’s called a 3-against-4 polyrhythm in Led Zeppelin’s 1975 song “Kashmir.” To practice it, count “ONE TWO three” with the guitar while a friend counts “one two THREE four” with the drums. The upper case letters indicate claps and the lower case letters indicate taps or silence. The resulting pattern repeats after twelve beats. (Variation – add an extra clap between beats ONE and TWO in every other repeat of the first pattern, so you’re clapping ONE-AND-TWO three FOUR FIVE six.)
Steve Reich’s “Clapping Music” uses a single repeated rhythm pattern. The two players start by clapping the 12-beat pattern together in unison. After eight measures, one performer shifts the pattern forward by one beat and they clap the new pattern for eight measures. This process is continued until the two patterns align again. Here’s a visualization. Reich says that the piece was inspired by the clapping patterns in traditional flamenco music of the Roma people in Andalusia, Spain.