The simultaneous playing of one rhythmic value – such as straight eighth notes – against another contrasting value – such as triplets. Long identified with ancient origins in African music, polyrhythms are common in twentieth-century music, from minimalist compositions to progressive rock and jazz.
It’s the interplay and juxtaposition of seemingly opposing rhythms that give polyrhythms their character. In other words, a drum solo that’s filled with lots of varying note values isn’t necessarily polyrhythmic unless those note values are being played at the same time. The most common polyrhythm is the juxtaposition of triplets against quarter or eighth notes. A common alternative to thinking of these patterns in musical notation is to envision (or hear) them as ratios: the triplet example would have a ratio of 3:2. Other simple polyrhythms are 3:4, 4:3, 5:4, 7:8 and so on.