Time Signatures
The time signature (also known as meter signature, metre signature, or measure signature) specifies how many beats (pulses) are to be contained in each bar and which note value is to be given one beat.
In a musical score, the time signature appears at the beginning of the piece, as a time symbol or stacked numerals, such as or 3/4 (read common time and three four time, respectively), immediately following the key signature or immediately following the clef symbol if the key signature is empty.
Time signatures consist of two numerals, one stacked above the other:
For instance, 2/4 means two crotchet beats per bar—3/8 means three quaver beats per bar.
Basic time signatures: 4/4, also known as common time ( ); 2/2, also known as cut time or cut-common time ( ); plus 2/4; 3/4; and 6/8.
Compound Time Signatures
In compound meter, subdivisions of the main beat (the upper number) split into three, not two, equal parts. Compound time signatures are named as if they were simple time signatures, in which the one-third part of the beat unit is the beat, so the top number is commonly 6, 9 or 12 (multiples of 3). The lower number is most commonly an 8 (an eighth-note): as in 9/8 or 12/8.
Example
3/4 is a simple signature that represents three quarter notes. It has a basic feel of (Bold denotes a stressed beat):
one two three (as in a waltz)
Each crotchet might comprise two quaver) giving a total of six such notes, but it still retains that three-in-a-bar feel:
one and two and three and 6/8
Theoretically, 6/8 can be thought of as the same as the six-quaver form of 3/4 above with the only difference being that the eighth note is selected as the one-beat unit. But whereas the six quavers in 3/4 had been in three groups of two, 6/8 is practically understood to mean that they are in two groups of three, with a two-in-a-bar feel (Bold denotes a stressed beat):
one two three, four, five, six.
