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Understanding time signatures

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Intro At the start of a piece of music, just after the clef, you will probably see a time signature such as 6/8. Or someone may say that a piece of music is in "six eight time". What do the 6 and 8 mean? To find out more

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  • The top number gives the number of beats in the measure
  • The bottom number indicates the note value - the type of note used to notate the rhythm (quarter note, eighth note etc).

Top number

This is the easy one. The top number gives the number of beats in the bar.
E.g. 3, 4 etc. So 4/4 has four beats to the bar, 3/4 has three, and 6/8 has six beats to the bar.

Here is a 4/4 rhythm, so with four beats to the bar.

Bottom number

The bottom number shows how the beats are notated. If it says /4 then they are notated as quarter notes (UK crotchets). It's /8 for eighth notes (quavers), and /2 for half notes (minims), /16 for sixteenth notes (semiquavers) and so on.

So in 4/4 each beat is notated as a quarter note, so the whole bar is notated as a whole note (UK sem-breve).

You could as easily notate it as 4/8 or as 4/2 (counting 4 half notes - or UK minims to a bar) etc. Your performers would play exactly the same rhythm for all of those. So you could say -who cares, why does it matter?

But it is most usual to use 4/4 for tunes with 4 beats to a bar. It is just a convention. It's not wrong though to use 4/8 or 4/2 for a tune with four beats to the bar. It's not like it's "misspelt" like that. Just eccentric to do it that way - you might want to do it like that for some good reason or other and if so no-one will say you are wrong to do it.

Compound time

What we have seen so far is simple time. Compound time is used for any music with a triplet feel to it. That is, a rhythm that you count as 1 & a 2 & a ...

If the tune has only occasional triplets, then you use a quarter note (crotchets) time signature e.g. 2/4, 4/4 etc. - that's simple time. In simple time, any triplets you need, you can just show individually as triplets with a 3 above the notes. Duplets can be shown as normal eighth notes (quavers).

But if the rhythm has many triplets, it is more convenient to do it the other way, use triplet eighth notes in the time signature and add a 2 above the notes if you ever need a duplet. So a jig is normally shown as 6/8. I.e. 6 of the eighth note beats to the bar.

Conducting pattern for 6/8

More videos for compound time rhythms

So, in compound time, by convention, you don't need to show triplets as triplets. This convention is used for 6/8 or other compound time signatures such as 9/8 or 12/8, any time signature with an 8 on the bottom and a multiple of 3 on the top.

This saves the typographer the need to write in "3"s on top of all the triplets. In 6/8 and other compound time signatures, that's taken for granted, instead you need to write a "2" on top if ever you have a duplet to play in the rhythm instead of a triplet.

That's what compound time is. It's music which is counted in threes, notated using eighth notes, and with the number of eighth notes in the bar divisible by three, with the convention that you don't need to write triplet signs over all the notes.

Ambiguous rhythms

Sometimes you don't know how to notate a rhythm. For instance, four triplets to a bar could be 12/8, or if it has occasional duplets, and enough of them, you might perhaps want to notate it as 4/4 with lots of triplet beats.

Ambiguous bars

Sometimes you may not be sure of the bar either. That same rhythm of 12/8 might also be two bars of 2/4 or two bars of 6/8.

The bars of a rhytm often group themselves together naturally in higher units. So 4/4 is often played in two bar pairs, and in higher groupings of 4, 8, 16 and even more bars.

It wouldn't be wrong to treat e.g. two bars of 4/4 as the bar beat. Since the middle beat of 4/4 is also emphasized, then you could treat it as a larger bar of four beats with each beat twice the size you had before - or notate it as 8/4.

You would still get a very similar rhythm like that. But often it is natural to use the smaller units for the bar line. The harmonic structure of the tune may more or less force it on you too. For instance if the tune uses one harmony for an entire bar, then changes on every bar, or the pattern of chords repeats for several bars, it may then be pretty clear where the bar-line should be shown.

Similarly, you could rarely divide into smaller rhythmic units for the bar line. E.g. you could notate 6/8 as two bars of 3/8 each (or even more eccentrically, two fast bars of 3/4). Again you have a natural accent anyway in the middle. Mainly it will depend on the harmonic or melodic structure of the piece, normally it will be clear from the tune or harmony that it "really is in 6 beats to the bar".

Composers can also deliberately make the bar-line ambiguous too using syncopation etc :-). Sometimes there may be no clear rhythm for quite a while as Stravinsky did in the Rite of Spring, playing with the rhythm so much that sometimes you can't pick out a bar line at all.

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