Time signature


A time signature is an indication in music notation that specifies how many note values of a particular type fit into each measure. The time signature indicates the meter of a musical movement at the bar level.
In a music score the time signature appears as two stacked numerals, such as , or a time symbol, such as . It immediately follows the key signature. A mid-score time signature, usually immediately following a barline, indicates a change of meter.
Most time signatures are either simple, or compound. Less common signatures indicate [|complex], [|mixed], [|additive], and [|irrational meters].

Time signature notation

Most time signatures consist of two numerals, one stacked above the other:
  • The lower numeral indicates the note value that the signature is counting. This number is always a power of 2, usually 2, 4 or 8, but less often 16 is also used, usually in Baroque music. 2 corresponds to the half note, 4 to the quarter note, 8 to the eighth note, 16 to the sixteenth note.
  • The upper numeral indicates how many such note values constitute a bar.
For instance, means two quarter-notes per bar, while means four eighth-notes per bar. The most common time signatures are,, and.

Symbolic signatures

By convention, two special symbols are sometimes used for and :
  • The symbol is sometimes used for time, also called common time or imperfect time.
  • The symbol is sometimes used in place of and is called alla breve or, colloquially, cut time or cut common time.
These symbols derive from mensural time signatures, described below.

Frequently used time signatures

Simple versus compound

Simple meters are those whose upper number is 2, 3, or 4, sometimes described as duple meter, triple meter, and quadruple meter respectively.
In compound meter, the note values specified by the bottom number are grouped into threes, and the upper number is a multiple of 3, such as 6, 9, or 12. The lower number is most commonly an 8 : as in or.
Other upper numbers correspond to irregular meters.

Beat and subdivision

Musical passages commonly feature a recurring pulse, or beat, usually in the range of 60–140 beats per minute. Depending on the tempo of the music, this beat may correspond to the note value specified by the time signature, or to a grouping of such note values. Most commonly, in simple time signatures, the beat is the same as the note value of the signature, but in compound signatures, the beat is usually a dotted note value corresponding to three of the signature's note values. Either way, the next lower note value shorter than the beat is called the subdivision.
On occasion a bar may seem like one singular beat. For example, a fast waltz, notated in time, may be described as being one in a bar. Conversely, at slow tempos, the beat might even be a smaller note value than the one enumerated by the time signature.
Mathematically the time signatures of, e.g., and are interchangeable. In a sense all simple triple time signatures, such as,,, etc.—and all compound duple times, such as, and so on, are equivalent. A piece in can be easily rewritten in, simply by halving the length of the notes.
\new Staff <<
\new voice \relative c'
\new voice \relative c
>>

Other time signature rewritings are possible: most commonly a simple time-signature with triplets translates into a compound meter.
\new Staff <<
\new voice \relative c'
\new voice \relative c
>>

The choice of time signature in these cases is largely a matter of tradition. Particular time signatures are traditionally associated with different music styles—it would seem strange to notate a conventional rock song in or, rather than.

Examples

In the examples below, bold denotes the primary stress of the measure, and italics denote a secondary stress. Syllables such as "and" are frequently used for pulsing in between numbers.
Simple: is a simple triple meter time signature that represents three quarter notes, usually perceived as three beats. In this case the subdivision would be the eighth note. It is felt as
Compound: Most often, is felt as two beats, each being a dotted quarter note, and each containing subdivisions of three eighth notes. It is felt as
The table below shows the characteristics of the most frequently used time signatures.

Tempo giusto

While changing the bottom number and keeping the top number fixed only formally changes notation, without changing meaning –,,, and are all three beats to a meter, just noted with eighth notes, quarter notes, half notes, or whole notes – these conventionally imply different performance and different tempi. Conventionally, larger numbers in the bottom correspond to faster tempi and smaller numbers correspond to slower tempi. This convention is known as tempo giusto, and means that the tempo of each note remains in a narrower, "normal" range. For illustration, a quarter note might correspond to 60–120 bpm, a half note to 30–60 bpm, a whole note to 15–30 bpm, and an eighth note to 120–240 bpm; these are not strict, but show an example of "normal" ranges.
This convention dates to the Baroque era, when tempo changes were indicated by changing time signature during the piece, rather than by using a single time signature and changing tempo marking.

Complex time signatures

Signatures that do not fit the usual simple or compound categories are called complex, asymmetric, irregular, unusual, or odd—though these are broad terms, and usually a more specific description is any meter which combines both simple and compound beats.
Irregular meters are common in some non-Western music, and in ancient Greek music such as the Delphic Hymns to Apollo, but the corresponding time signatures rarely appeared in formal written Western music until the 19th century. Early anomalous examples appeared in Spain between 1516 and 1520, plus a small section in Handel's opera Orlando.
The third movement of Frédéric Chopin's Piano Sonata No. 1 is an early, but by no means the earliest, example of time in solo piano music. Anton Reicha's Fugue No. 20 from his Thirty-six Fugues, published in 1803, is also for piano and is in. The waltz-like second movement of Tchaikovsky's Pathétique Symphony, often described as a "limping waltz", is a notable example of time in orchestral music.
\relative c

Examples from 20th-century classical music include:
In the Western popular music tradition, unusual time signatures occur as well, with progressive rock in particular making frequent use of them. The use of shifting meters in The Beatles' "Strawberry Fields Forever" and the use of quintuple meter in their "Within You, Without You" are well-known examples, as is Radiohead's "Paranoid Android".
Paul Desmond's jazz composition "Take Five", in time, was one of a number of irregular-meter compositions that The Dave Brubeck Quartet played. They played other compositions in , , and , expressed as. "Blue Rondo à la Turk" is an example of a signature that, despite appearing merely compound triple, is actually more complex. Brubeck's title refers to the characteristic aksak meter of the Turkish karşılama dance.
However, such time signatures are only unusual in most Western music. Traditional music of the Balkans uses such meters extensively. Bulgarian dances, for example, include forms with 5, 7, 9, 11, 13, 15, 22, 25 and other numbers of beats per measure. These rhythms are notated as additive rhythms based on simple units, usually 2, 3 and 4 beats, though the notation fails to describe the metric "time bending" taking place, or compound meters. See [|Additive meters] below.
Some video samples are shown below.

Mixed meters

While time signatures usually express a regular pattern of beat stresses continuing through a piece, sometimes composers change time signatures often enough to result in music with an extremely irregular rhythm. The time signature may switch so much that a piece may not be best described as being in one meter, but rather as having a switching mixed meter. In this case, the time signatures are an aid to the performers and not necessarily an indication of meter. The Promenade from Modest Mussorgsky's Pictures at an Exhibition is a good example. The opening measures are shown below:


Igor Stravinsky's The Rite of Spring is famous for its "savage" rhythms. Five measures from "Sacrificial Dance" are shown below:
In such cases, a convention that some composers follow is to simply omit the time signature. Charles Ives's Concord Sonata has measure bars for select passages, but the majority of the work is unbarred.
Some pieces have no time signature, as there is no discernible meter. This is sometimes known as free time. Sometimes one is provided so that the performer finds the piece easier to read, and simply has "free time" written as a direction. Sometimes the word FREE is written downwards on the staff to indicate the piece is in free time. Erik Satie wrote many compositions that are ostensibly in free time but actually follow an unstated and unchanging simple time signature. Later composers used this device more effectively, writing music almost devoid of a discernibly regular pulse.
If two time signatures alternate repeatedly, sometimes the two signatures are placed together at the beginning of the piece or section, as shown below: