Audio: polyrhythm (0:08)
polyrhythm plays polyrhythm. The polyrhythm figure shows the score is played by three percussion instruments:
Polyrhythm consists of two or more simultaneous and different rhythms.
Polyrhythm can be used for a short duration, one or two bars, or for a whole piece, in which case it is also known as cross-rhythm.
Polyrhythm adds contrast and tension to a piece of music. Contrast arises from the use of different meters, tension arises because the meters can be interpreted at different tempi. The low tom rhythm in the top part of polyrhythm is your standard 4/4 meter at 120 bpm. The contrasting rhythm on the conga in the middle part consists of six beats in two groups of three, which could be treated as a 4/4 meter at 120bpm or as a 6/8 meter at 180bpm.
polyrhythm is an example of the most common form of polyrhythm, informally known as three over two (3:2), formally as hemiola. It consists of a pair of rhythms in which one rhythm plays three beats while the other plays two. Such a simple idea produces rhythm of great subtlety.
Polyrhythm is not limited to 3:2. There are 4:3 polyrhythms and 5:4 polyrhythms and other esoteric permutations.