Time signature

The time signature is used in Western musical notation to specify the basic meter of a piece of music. Time signatures are written similarly to a fraction eg. 4/4 -- but is not, and is never written as such on a staff. In "simple" time signatures, the denominator indicates which note is the beat, that is, which note is to be stressed. If the denominator is 2, the half note or minim is one beat; if the denominator is 4, the quarter note or crotchet is one beat; and so on. The "numerator", the upper number indicates the number of beats in each measure. Examples of simple time signatures include "4/4" ("common time"), "2/2" ("cut time"), "3/4", "5/4", "2/4", and so on.

Time signatures where the number above is a multiple of three (excluding the number 3 itself) are often "compound" time signatures. In a compound signature, the lower number does not specify which note is the beat. Instead, each beat is divided into three sub-beats, and the denominator of the time signature determines what sort of note makes up a sub-beat. In "6/8" time, the sub-beats are eighth notes, and three of them make up a single beat. This means that the beat is a dotted-quarter note, and there are two beats in a measure. Other examples of compound time signatures include "9/8", "6/16", and so on. It is not uncommon for listeners to confuse a 3/4 (simple) time signature with a 6/8 (compound) signature, if the former is played rapidly, or the latter is played slowly.

Pieces with two beats to the bar, such as 2/4 or 6/8, are said to be in duple meter. Similarly, music with three beats to the bar (such as 3/2 or 9/8) is in triple meter. Music with four beats to the bar is in quadruple meter, five beats is quintuple meter and seven is septuple meter. These names can be combined with the simple and compound terms, so that 3/4 time can be described as simple triple, 6/8 as compound duple and so on.

Time signatures can be much more complex than notating the stressed beats in a bar. The signature

means that the first of a group of three quavers (eighth notes) is to be stressed, then the first of a group of two, then first of a group of three again. The stress pattern is usually counted as one-two-three-one-two-one-two-three, italics indicating stresses. This kind of time signature is common in folk and non-Western types of music.

In modern Western Music, in styles such as serialism and minimalism, the time signature is often avoided entirely, or, the key signature as well might be omitted. An underlying time signature or key may be present, but it may be too notationally complex or too redundant to notate these details. In other cultures, time is maintained not by a defined notation, but by a drum or other percussion instrument. Examples of this can be found in Indian classical music (see Indian music) and gamelan music, both of which often rely on oral tradition to pass down popular songs, rather than notation, as in Western classical music (see Western music).

Some standard time signatures in Western music are

4/4 or C -- common time
1/1 -- used very rarely, several times by Edward Elgar in several of his studies.
2/2 or ¢ -- cut time, used for marches
4/2 -- alla breve
2/4 -- used for polkas or marches
3/4 -- used for waltzes, minuets and scherzi
6/8 -- used for fast waltzes or marches
5/4 -- used for Dave Brubeck's "Take Five" and the original versions of the theme from Mission: Impossible¹. It is also used in classical music by Gustav Holst in "Mars" from The Planets. 5/4 is usually grouped as 3+2 or 2+3.
7/4 -- used for "Money" by Pink Floyd, numerous Genesis songs and "The Unsquare Dance" by Dave Brubeck.

Other meters are sometimes encountered as well. Dave Brubeck in particular made use of unusual time signatures in his music.