Earlier I posted about simple meter: https://functionalanalysis.blog/2017/10/24/simple-meter/ and today I want to write about another common type of meter, compound meter. Remember that Time signatures are a purely visual phenomenon – how we write music out on a page. Meter is aural – how you hear it. Generally, these two things match, but sometimes there are reasons they don’t. Also, there are more different ways of writing out time signatures then there are types of meter.
Compound meter is meter that primarily divides into groups of three. The most common example of compound meter is the 6/8 (six-eight) time signature. All compound meters have a top number that is a multiple of three, and the bottom instead of showing the primary beat unit, shows the primary subdivision.
So, the primary beat above is a dotted quarter, but since most people don’t use half/dotted units in time signatures,[*] the time signature shows eighths. To get the number of beats in a measure, divide the top number by 3. Six divide by three is 2, so this is a compound duple meter. Other examples of time signatures for compound duple would be 6/4, 6/16, 12/4 or 12/8. An aural example of this is Between, by Natalie Haas: (steady tempo starts about 0:38) https://www.youtube.com/watch?v=1-CTEsCgfUE
Like with simple meters, the duple or triple shows whether the number of beats is divisible by two or three. So a common time signature for compound triple meter is 9/8:
While 9/8 is probably the most common time signature for compound triple, 9/4, 9/16 and anything else with 9 on top would also work. I learned today that slip jigs, a type of Irish tune, are in compound triple.[†] An famous aural example is The Rocky Road to Dublin: https://www.youtube.com/watch?v=iZ6uEaigbuw
[*] tho some argue that we should show the bottom with the note itself rather than a number, but now I can’t find the picture I’m thinking of