- Richard Rastall
In Western notation a sign or signs placed at the beginning of a composition, after the clef and any key signature, or in the course of a composition. It indicates the Metre of the piece or a change in metre for a part of the piece. In modern usage two figures are usually given, one above the other: the lower indicates the unit of measurement, relative to the semibreve; the upper indicates the number of units in each bar. Thus a signature of 3/2 indicates that there are three minims (‘half-notes’) in each bar; a signature 9/8 indicates that there are nine quavers (‘eighth-notes’) in each bar.
Some signatures are survivors of the system of proportions and mensuration signs (see Notation:
is used for 4/4 and
for 2/2 (also called alla breve).
is a relic of the medieval tempus imperfectum cum prolatione minore, a mensuration where each long contained two breves and each breve contained two semibreves. The sign...