A tuplet (also irrational rhythm) specifies a change in the number of expected subdivisions for a given pulse as set forth by the type of meter (simple or compound). For example, in a 2/4, a simple binary meter,  time is subdivided in multiples of two, and so, the quarter note (the beat unit in 2/4 ) is expected to subdivide in two eighth notes. A tuplet of three eighth notes (triplet) changes the number of subdivisions, allowing to specifically represent the moment when the reference beat sub-division becomes three eighth notes instead of two expected in a simple meter (figure 7a); in a 3/8 meter (simple ternary), the eighth note (beat unit) is expected to subdivide in two 16th notes and four 32th notes.

A tuplet of five 32th notes (quintuplet) indicates that the number of subdivisions has been changed from four to five 32th notes (figure 7b); in a 6/16 meter (compound binary), the dotted eighth note (beat unit) is expected to subdivide in three 16th notes, each 16th note in four 64th notes. A tuplet of five 64th notes (quintuplet) subdivides the time of a 16th note in five 64th notes rather than the regular subdivision by four (figure 7c). Tuplets can also call for a number of subdivisions that is smaller than what is expected. In figure 7d, the beat unit of a 9/8 (dotted quarter note) subdivides in three eighth notes. The duplet of eighth notes is to be played in the time of the three eighth notes that originally divided the beat unit.