Compound meters are meters in which the beat is divisible by 3.
You can easily tell if a meter is a compound meter by the top number of the time signature. The top number can be any number divisible by 3 that is greater than 3. If the top number is 6, 9 or 12 then the meter is a compound meter.
The beat in a compound meter will divide in to 3 equal parts. Since the beat divides in to 3 equal parts, the beat in any compound meter will always be some type of dotted note.
Lets take a look at an example in 6/8 to demonstrate this.
In a measure of 6/8 it is true that 6 1/8 notes will fill up a measure. But this does not mean that there are 6 beats in 6/8.
To determine the number of beats in any compound meter begin by looking at the top number.
Since the top number is 6, we know it is a compound meter. To find the number of beats divide the top number by 3. This will show us that in 6/8 there are 2 beats.
To find the length of a beat multiply the note value represented by the bottom number by 3. To find this imagine the bottom number as a fraction under the number 1. In this case 1/8 equals an eighth note.
Now multiply an eighth note by 3, which will equal 1 1/2 beats, or a dotted quarter note.
So the beat in 6/8 is the dotted quarter note, and since there are 2 beats in 6/8 two dotted quarter notes will fill up a measure of 6/8.
To help you remember and more easily see this this information visually, you can download the free Compound Meter poster.
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