## Time signature

• A time signature is a set of two numbers (or sometimes an abbreviation for them) which is given at the beginning of a piece of music to indicate the number of beats in a bar and the type of these beats.
• A new time signature can also appear at other places in the music where the number of beats per bar or the type of beats changes, in which case the new time signature applies from that point onwards.

• A time signature is always written on a stave, with the upper number (the number of beats per bar) occupying the top two spaces, and the lower number (indicating the type of the beats) in the bottom two spaces:
Although they appear as one number above the other, the numbers do not represent a fraction; the two numbers just have different meanings.

• When it appears at the beginning of a piece, the time signature is written after the clef, and immediately after the key signature (if there is one):

• When it appears in the middle of a piece, it always appears at the beginning of a new bar, immediately after the bar line.
• If the change happens to be at the beginning of a new line, the new time signature is normally written at the end of the previous line as well as the beginning of the new line.

• The top number is simply the number of beats in each bar; the bottom number indicates the length of each beat in terms of its note length, as follows:
• 2 = minim (half-note - see alternative names)
• 4 = crotchet (quarter-note)
• 8 = quaver (eighth-note)
These are simply representations of the note lengths; the numbers have no particular significance in themselves.
• Those people who are used to the name quarter note for crotchet may find it helpful to think of the 4 at the bottom as a representation of a fraction, but only as an aide-memoire - it is not really a fraction.

• The numbers are normally written in an old fashioned font in which the figure 2 and 3 are very curly. The 4 printed is almost always a rather strange one, see the examples here.

• The time signature not only gives the number and type of beats, but also implies the sub-division of the bar. This in turn implies that some beats in the bar are stronger than others. It also implies the grouping of notes and rests.

• Time signatures can be categorised as follows:

1. According to the sub-division of the beat:
• Simple time - this is when the beat can be subdivided into halves
• Compound time - this is when the beat can be subdivided into thirds - the time signature is written as if the subdivision is the main beat, but in fact the main beat is three times slower

2. According to the number of beats per bar:
• Duple time - two beats per bar - the first is strong, the second weak ("left, right, left, right")
• Triple time - three beats per bar - the first strong, the second and third weak ("Oom pah pah")
• Quadruple time - four beats per bar - the first strong, the third less strong, and second and fourth weak ("Simple Simon met a pie man")

• Combining these two types of categorisations, the following possibilities emerge:

1. Simple duple
• 2/2 = 2 minims per bar ("Alla Breve" - see below)
• 2/4 = 2 crotchets per bar
2. Simple triple ("Waltz time")
• 3/2 = 3 minims per bar
• 3/4 = 3 crochets per bar
• 3/8 = 3 quavers per bar
• 4/2 = 4 minims per bar (see "Alla breve" below)
• 4/4 = 4 crotchets per bar ("Common time" - see below)
• 4/8 = 4 quavers per bar
4. Compound duple
• 6/4 = 2 beats per bar, each of 3 crotchets - unusual nowadays
• 6/8 = 2 beats per bar, each of 3 quavers - quite common today
5. Compound triple
• 9/4 = 3 beats per bar, each of 3 crotchets - very rare
• 9/8 = 3 beats per bar, each of 3 quavers - occasionally seen
• 12/4 = 4 beats per bar, each of 3 crotchets - very rare
• 12/8 = 4 beats per bar, each of 3 quavers - very rare

• Abbreviations:
• 4/4 is known as "Common time". It is often seen as 4/4, but it can be written on the stave as a large C. There are four crotchets in every bar.
• 2/2 is known as "Alla breve" (although strictly "Alla breve" is 4/2) and is sometimes written as a large C with a vertical line through it. There are two minims in every bar.

• Other combinations are possible, but unusual:
• 5/4 - 5 crotchet beats per bar
• 7/4 - 7 crotchet beats per bar
• Almost any other combination of numbers you could imagine...

• It is even possible to have two time signatures specified, one after each other at the beginning of the piece. This normally means that the two time signatures specified apply to alternate bars, but this is very unusual, and only seen in 20th century music.

• Some music is written without a time signature at all. For example, plainsong, sung by monks for hundreds of years, is without any strict rhythm, and although it may have accents, they do not come regularly, so it is not possible to specify a time signature.

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