Quadruplet
Four notes in the value of three.
What it means
A quadruplet divides a note value into four equal parts where, according to the prevailing order, three would stand. It thus belongs among the irregular divisions and occurs, like the duplet, in triple-based contexts: in six-eight, nine-eight, or twelve-eight time, or in the division of a dotted note.
In the notation
Above or below the group stands the figure 4, usually with a bracket or slur. The four notes are written in the value that would give three without the figure: in six-eight time, four eighths marked as a quadruplet replace the three eighths of one beat. Each therefore lasts three-quarters of an ordinary eighth. The notation with a figure is preferred to the computationally equivalent alternative, because it makes the relation to the beat visible.
Musical use
The effect arises from the contradiction: in a triple-based flow, a sudden fourfold division creates an urgency, because the notes follow one another more densely than expected. Conversely, the duplet in the same surroundings seems broader. If both divisions run simultaneously in different voices, the ratio three against four results, one of the more difficult forms of polyrhythm.
The quadruplet is to be distinguished from the ordinary fourfold structure in duple time signatures: there the fourfold division is the rule and needs no figure. A quadruplet exists only where three would be the norm.
Quadruplets stand in time signatures with a threefold beat, for instance in 6/8 time, and divide a dotted quarter into four equal parts. They are usually written as four sixteenths or eighths with a figure 4. As with all such tuplets, there are various spellings; some editions prefer dotted values.
Performance practice
Determine first what total value the group fills, and distribute the four notes evenly over it — not as three plus one appended. Practise slowly against a metronome that beats only the beat, not the subdivisions. With three against four, secure both layers separately first and join them very slowly; the shared reference point is the beginning of the beat. And keep counting in the overarching unit, otherwise the flow stalls.