Polyrhythm
A polyrhythm is two or more independent rhythms played at the same time. A simple example of a polyrhythm is 2 against 3: both rhythms are simple pulses, but the 3-beat pattern is faster than the 2-beat pattern, so that they both take the same amount of time. Other simple polyrhythms are 3 against 4, 4 against 5, 4 against 7, etc. Traditional African music is heavily polyrhythmic, although, unlike below, the downbeats do not usually coincide. The death metal band Meshuggah also have complex polyrhythms in their music. Much minimalist and totalist music makes extensive use of polyrhythms.
The following is an example of a 2 against 3 polyrhythm, given in time unit box system (TUBS) notation; each box represents a fixed unit of time; time progresses from the left of the diagram to the right, although this is irrelevant since the pattern is symmetric. Beats are indicated with an X; rests are indicated with a blank.
Examples
| 2-beat rhythm | X | X | X | X | X | X | X | X | ||||||||||||||||
| 3-beat rhythm | X | X | X | X | X | X | X | X | X | X | X | X |
A common memory aid to help with the 2 against 3 polyrhythm is that it has the same rhythm as the phrase "not difficult"; the simultaneous beats occur on the word "not"; the second and third of the triple beat land on "dif" and "cult", respectively. The second 2-beat lands on the "fi" in "difficult." Try saying "not difficult" over and over in time with the sound file below. Another phrase with the same rhythm is "cold cup of tea."
Similar phrases for the 3 against 4 polyrhythm are "pass the gosh darn butter" and "what atrocious weather"; The 3 against 4 polyrhythm is shown below.
| 3-beat rhythm | X | X | X | X | X | X | ||||||||||||||||||
| 4-beat rhythm | X | X | X | X | X | X | X | X |
As can be seen from above, the counting for polyrhythms is determined by the lowest common multiple, so if one wishes to count 2 against 3, one needs to count a total of 6 beats, as lcm(2,3) = 6 (123456 and 123456). However this is only useful for very simple or polyrhythms, or for getting a feel for more complex ones, as the total number of beats rises quickly. To count 4 against 5, for example, requires a total of 20 beats, and counting thus slows the tempo considerably. However some players, such as classical Indian musicians, can intuitively play high polyrhythms such as 7 against 8.
Below are some example polyrhythms in MIDI format:
