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I know the general idea behind time signatures:

6:8 is 6 eighth notes in a bar, 3:4 is 3 quarter notes in a bar.

I also understand that in situations like these, while the two technically equal each other mathematically, they have different stressed beats.

However, I'm confused as to how these stressed beats are found. In other words, what if I was given a time signature like 12:8? 4:2?

I've heard the rule that in x:8 time, there are always groups of three, but what else do you have to go by?

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The simplest way to derive which beats are stressed in a given time signature is to look at how the notes are beamed or agogically accented.

For example, 6/8 is typically divided in a 3+3/8 grouping (as noted in other answers), however, it could also be grouped 2+4/8, 1+5/8, 4+2/8, and 5+1/8 for example. Each of these different divisions stresses a different beat in the measure, and must be grouped accordingly. Through notation, you can distinguish groupings through how notes are beamed.

This grouping tactic is even more pronounced in asymmetric meters, like 5/8 and 7/8. In these groupings the stresses must become lop-sided, so a 5/8 typically turns into a 2+3/8 or a 3+2/8.

If the time signature doesn't allow for beamed groupings (such as 7/4), then it is important to look at phrasing, and if possible, agogic accents. If in 7/4 I saw two half-notes followed by three quarter-notes, I would know that it had a 4+3/7 grouping.

Alternatively, look at phrase or slur markings to help you distinguish which beats begin / end phrases. Look at other instruments (if available) in the score to see if another part can clarify the confusing grouping. Listen to other recordings and see how others have phrased it. Lastly, play through it and figure out which phrasing sounds good to you.

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In 6/8, the unit of beat is the dotted quarter note, so you have two beats that are divided into triplets - that's to say that you would count the beats something like "One-two-three, two-two-three." It's duple (or two beat) time, but the beats themselves are divided by three. In 3/4 time, there are three quarter note beats to the bar, divided into two eighths apiece.

In 12/8 time, the unit of beat is also a dotted quarter note, so you have something with a beat pattern like 4/4 time (four beats to the bar, with a stress on the first beat and a lesser stress on the third), but each beat is divided into triplet eighths rather than duplets.

In general, if the number of beats (the top of the time signature) is divisible by three more than once (which means that time signatures like 3/4 and 3/8 don't apply here), you have a time signature where the unit of beat is equal to the three of the note values specified by the bottom of the time signature. Thus you can have a time signature of 15/16, which means you have 5 beats, each with a note value of a dotted eighth, or 6/4, which means two beats, each with a note value of a dotted half note.

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    I think "divisible by 3 more than once" usually means "divisible by 9"; I suggest "a multiple of 3". Even so, 3/8 can sometimes be '1 to a bar'. Also, 15/8 can also be 3 beats, each 5/8, e.g. Scriabin's prelude op. 11 no. 14. So it is necessary to look intelligently at the music to be sure. – Brian Chandler Dec 24 '14 at 10:24
  • Thank you, you are right about multiple of threes - I was struggling for the best way to exclude 1 x 3, because, properly speaking, any time signature can be one to the bar at a fast enough tempo, but they still have divisions within the bar. If every bar has a single note per bar, then someone is committing an atrocity of notation. (cont'd...) – user16935 Dec 24 '14 at 11:41
  • The normal convention, I believe, is to take the lowest common denominator as the prevailing tuplet. The 15/8 case you mention would normally be written as 5 against 4 in standard triple time, and, indeed, I seem to recall a late Scriabin étude that did just that (against triplets in the left hand). I'd have to dig out my Dover edition of the preludes and études to be sure... – user16935 Dec 24 '14 at 11:45
  • @Patrx2 Thank you! Best explanation so far (unfortunately since I'm a new member I can't vote up your answer), but I'm still a bit confused. I'm starting to understand individual time signatures that I've been working with like of course 12:8 and 6:8 but my original goal was to learn how to work with an unknown one. You said that being divisible by 3 two times (9) makes the "unit of beat is equal to the three of the note values specified by the bottom of the time signature." But then you used 15/16 as an example...And what if I was given a time signature like 12:4 or 11:2? – cbarkachi Dec 24 '14 at 12:25
  • And I believe I also saw you mention the lowest common denominator. So in let's say, 6:4 time, it would be 6 quarter notes (crotchets?), but with 2 (common denominator) as the unit of the beat, therefore making it 3 groups (triple?) of 2 quarter notes...? Again thank you, sorry if these questions seem pitiful! – cbarkachi Dec 24 '14 at 12:34
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NO! 6/8 is not six groups of quavers it is compound duple time with each bar consisting of a dotted crotchet. If you group six quavers together it implies 3/4 time.

12:8? Here you have compound Quadruple time with each beat consisting of a dotted crotchet

4:2? Here you have four groups of minims

Now let us think critically of what a time signature is. Time signatures at is very root try to explain to you the amount of time or notes that the bars of the music should have.

There is two numbers but what do they mean I can hear you ask? Well the first number tells us how many groups of notes we have and the second tells us what each group consists of.

So let us take 2/4 time as an example. The first number tells us the number of groups ie 2 and the second number tells us that the groups consist of crotchets ( 2 = minims 4 = crotchets 8 = quavers)

But wait there is more. There is a second type of Time signatures. They are called compound time signatures. No all these do is add dots to our groups but for the most part the same effect applies.

6/8 is compound duple time with groups of dotted crotchets. 9/8 is compound triple time with beats of dotted crotchets and so on and so forth.

Hope that helped.

  • Yes. If 6/8 is "six eighths in the bar" so is 3/4. But in fact 3/4 is "three quarter-notes in the bar", 6/8 is "two dotted quarters in the bar". Convention, as much as arithmetic. – Laurence Payne Mar 8 '15 at 1:38

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