Duplet
Two notes in the time of three of the same kind.
What it means
A duplet divides a beat that is inherently in three into two equal parts. It is thus the counterpart to the triplet, which divides a beat in two into three parts. It can therefore occur only in metres with a beat in three — in 6/8, 9/8, or 12/8 time — or where a dotted note is divided.
In the notation
Above or below the group stands the numeral 2, usually with a bracket or a slur. The two notes are written in the value that without the numeral would yield three notes: in 6/8 time, two eighth notes marked as a duplet replace the three eighth notes of a beat, so each lasts one and a half ordinary eighth notes. Equivalently one could write dotted sixteenth notes; the duplet notation is preferred because it makes the relation to the beat clearer. Occasionally, instead of the 2, the numeral 4 is found for a corresponding division in four.
Musical use
The duplet unfolds its effect through the contradiction with its surroundings: in a flow that is in three throughout, a sudden division in two seems broader, calmer, occasionally also heavily stressed. If both divisions run simultaneously in different voices, the ratio two against three arises, one of the basic forms of polyrhythm.
The duplet is to be distinguished from mere dotting: the latter lengthens a value within the prevailing division, the former sets a different division against it.
Duplets are used in metres with a beat in three, that is, in 6/8, 9/8, and 12/8, when a beat is to be divided into two equal parts. In notation, two eighth notes stand with the numeral 2; some editions write instead two dotted eighth notes, which represent the same rhythm without a numeral.
Performance practice
Practise two against three by taking both hands separately at first and then very slowly together; the common reference point is the beginning of the beat, and in between the duplet note lies exactly in the middle. A spoken mnemonic helps as long as it does not become a crutch. Keep counting in the superordinate beat, not in the subdivisions — otherwise the flow stalls.