The time signature (also known as "meter signature") is a notational device used in Western musical notation to specify how many beats are in each bar and which note value (quaver, crotchet, quarter note and so on) constitutes one beat.

Most time signatures comprise two numbers, one above the other. (When writing about time signatures, time signatures are generally written with the top number separated from the bottom by a slash (in the manner of a fraction). The example here, for example, can be written 3/4.)

In a musical score, the time signature appears at the beginning of the piece, immediately following the key signature (or immediately following the clef if there is no key signature). A mid-score time signature indicates a change of meter.

Time signatures can be "simple" or "compound". In simple time signatures, the upper number indicates how many beats there are in a bar, and the lower number indicates the length of that beat. The most common simple time signatures are 2/4, 3/4, and 4/4.

Compound time signatures are distinguished by a top number which is 6 or above and a multiple of three (most commonly 6, 9, or 12). Unlike simple time signatures, the upper lower and lower numbers in compound time signatures do not represent the number of beats per measure and the duration of the beat. To determine the number of beats per measure for a compound time signature, divide the upper number by three. For example, in 6/8, there are 2 beats per measure (because 6 divided by 3 equals 2). The duration of the beat (or the "beat unit") in compound time is three times the duration represented by the lower number. For example, in 6/8, the beat unit is a dotted quarter-note (because three times the value of an eighth-note is a dotted quarter-note).

In compound time, the beat unit is always a dotted value. In simple time, the beat unit is always an undotted value.

For all meters, the first beat (the "downbeat") is stressed; in time signatures with four groups in the bar (such as 4/4 and 12/8), the third beat is also stressed, though to a lesser degree. This gives a regular pattern of stressed and unstressed beats.

To indicate more complex patterns of stresses, such as additive rhythms, more complex time signatures can be used. For example, the signature

which can be written 3+2+3/8, 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 classical music, Béla Bartók and Olivier Messiaen are composers to use such time signatures.

In some cases, the letter C (common time) is used in place of the 4/4 time signature. A similar C with a vertical line through it can be used in place of 2/2, indicating alla breve (cut time) for a fast duple meter.

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.

There is a sense in which all simple triple time signatures, be they 3/8, 3/4, 3/2 or anything else, and all compound duple times, such as 6/8, 6/16 and so on, are equivalent - a piece in 3/4 can be easily rewritten in 3/8 simply by halving the length of the notes. Sometimes, the choice of bass note is simply down to tradition: the minuet, for example, is generally written in 3/4, and though examples in 3/8 do exist, a minuet in 3/2 would be highly unconventional. At other times, the choice of bottom note can give subtle hints as to the character of the music: for example, time signatures with a longer bass-note (such as 3/2) can be used for pieces in a quick tempo to convey a sense of the time flying by.

Similarly, a piece in 2/4 can often sound like it is in 4/4 (or vice versa) and a piece in 3/4 can sound like it is in 6/8 or 12/8 time, particularly if the former is played quickly or the latter slowly.

In modern Western Music, in styles such as serialism and minimalism, the time signature is often avoided entirely (the key signature is also frequently omitted). An underlying time signature or key may be present, but it may be too notationally complex or too redundant to indicate. In the music of many cultures, time is maintained 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 (although both utilize an idiosyncratic rhythmic notation).

Standard time signatures in Western music include:

• 4/4 or C -- common time; very common in classical music; the norm in rock, jazz, country, and bluegrass
• 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, scherzi, and country & western ballads. Some rare examples of 3/4 in rock songs are "Manic Depression" by Jimi Hendrix, the middle section of the instrumental "Orion" by Metallica, and the first section of "In that quiet earth" by Genesis, the instrumental "Hell's Kitchen" by Dream Theater, and Part VII, "The Crimson Sunset", of the epic A Change of Seasons by the same band. (The sudden time change from 12/8 to 3/4 creates an eerie sensation of "time running out".)
• 6/8 -- used for fast waltzes or marches
• 9/8 -- indicates "compound triple time"
• 12/8 -- common in blues and doo-wop

Some unusual time signatures in Western music are:

• 5/4 -- also known as "quintuple meter," grouped as either (3+2) or (2+3). The first notable use of 5/4 in Western music was by Tchaikovsky in his "Pathetique" Symphony. 5/4 also appears in The Dave Brubeck Quartet's "Take Five"; the original versions of the theme from Mission: Impossible¹, YYZ (the intro only) by Rush, the slow movement of the "Sonata Mexicana" by Manuel Ponce, "Mars" from The Planets by Gustav Holst, "Face Dances Part Two" by Pete Townshend, "Living in the Past" by Jethro Tull, "The Grudge" by Tool, "Seven Days" by Sting, and "Kagura's Theme" from InuYasha by Kaoru Wada .

• 7/4 -- appears in "Money" by Pink Floyd, "Hello Radio" by They Might Be Giants, numerous Genesis and especially Rush songs, "Unsquare Dance" (2+2+3) by Dave Brubeck, "Rendez-vous 6:02" by UK, "Yellow Snow" by Frank Zappa, "The Munificent Seven" and "Saint Augustine in Hell" by Sting. The British TV show The Bill featured theme music in 7/4 for many years until it was remixed. Another mix has subsequently been produced which again uses 7/4. John Lennon's "All You Need is Love" features a changing meter (7/4 and 4/4 for the verses, 4/4 for the choruses).
• (5+6)/4 -- Pictures at an Exhibition theme by Modest Mussorgsky:

• 15/4 -- "The Wait" by The Pretenders
• (3+2+4)/8 -- "Supper's Ready" (the "Apocalypse in 9/8" section) by Genesis
• 14/16 -- "Mad Rush" by Philip Glass
• (2 1/2)/4 -- used by Carlos Chávez in his Sonata No. 3 (1928) IV, m. 1.

Other unusual meters exist. Dave Brubeck is well known for his employment of unusual time signatures (see above); Don Ellis consistently explored this area also. Progressive rock, progressive metal, and modal jazz often employ unusual time signatures. The group Stereolab have made extensive use of unusual time signatures, as have Nels Cline and Nick Didkovsky 's Doctor Nerve . In electronic music, Venetian Snares uses 7/4 and 5/4 almost exclusively. Many songs in Bertolt Brecht's plays feature no time signature at all; each measure contains a different number of beats. Burt Bacharach's rhythmically exciting song ""Promises, Promises"" likewise features a constantly changing meter. Igor Stravinsky's The Rite of Spring is famous for its "savage" rhythms:

¹ The theme songs from the M:I feature films (1996 and 2000) use 4/4 by repeating the first three beats of the bass line twice, holding melody notes during that period, and halving each note's duration.

External links

• Grateful Dead songs with unusual time signatures http://www3.clearlight.com/~acsa/rhythm.htm
• Doctor Nerve: Skin Scorebook http://www.doctornerve.org/nerve/pages/scorbook.shtml featuring a score which uses unusual time signatures

Musical notation
Staff : Clef | Key signature | Time signature | Note | Rest | Tempo | Dynamics | Leger lines
Note length : Longa | Breve | Semibreve | Minim | Crotchet | Quaver | Semiquaver | Demisemiquaver | Hemidemisemiquaver