Metre (music)

Metre is the measurement of a musical line into units such as beats and measures, indicated in Western notation by a symbol called a time signature. Properly, "metre" describes the whole concept of measuring rhythmic units, but it can also be used as a specific descriptor for a measurement of an individual piece as represented by the time signature -- for example, "This piece is in 4/4 metre" is equivalent to "This piece is in 4/4 time" or "This piece has a 4/4 time signature."

There are four different types of metre: simple duple (ex. 4/4), simple triple (ex. 3/4), compound duple (ex. 6/8), and compound triple (ex. 9/8). If each beat in a measure is divided into two parts, it is simple meter, and if divided into three it is compound. If each measure is divided into two beats, it is duple meter, and if three it is triple. Some people also label quadruple, while some consider it as two duples. The latter is more consistent with the above labeling system, as any other division above triple, such as quintuple, is considered as duple+triple (12123) or triple+duple (12312), depending on the accents in the musical example. However, in some music a quintuple may be treated and perceived as one unit of five, especially at faster tempos.

Most popular music is in 4/4 time, though often may be in 2/2 or cut time such as in bossa nova. Doo-wop and some other rock styles are frequently in 12/8, or may be interpreted as 4/4 with heavy swing. Similarly, most concert music before the 1900's was in 4/4, 3/4, 6/8 or other simple metre. More recent concert music switches meter frequently, such as some music by Igor Stravinsky; has no meter at all, such as drone based music exemplified by La Monte Young; or is based on additive rhythms, such as some music by Philip Glass.