isorhythm
A medieval compositional technique in which a fixed rhythmic pattern is repeated independently of the melodic pattern
In Depth
In isorhythm, the rhythmic pattern (talea) and the pitch pattern (color) are separate entities that cycle at different rates, creating complex overlapping structures. If the color has 12 notes and the talea has 8, they will not realign until 24 notes have passed. Guillaume de Machaut perfected the technique in his motets and Mass. Isorhythm anticipated 20th-century serial techniques by treating rhythm as an independent parameter, and composers like Messiaen directly acknowledged the connection.
Messiaen's use of non-retrogradable rhythms and modes of limited transposition is a direct descendant of medieval isorhythmic thinking.