Simple meter:

The simplest way to explain a simple meter is that each beat in a simple meter is felt separately. The most common ones are 4/4, 3/4 and 2/4. On 4/4 we have 4 counts per bar and each count is a quarter note. But when playing this, we can easily feel each beat separately, count each beat separately, tap each beat separately and  hence they are dubbed as simple meters. Along with 4/4, 3/4 and 2/4 we can also label 4/2 and 4/8 as simple meters. For example, 4/2 would be 4 half notes per bar. You can still feel and count each note separately but the note duration is a little longer. So one count in 4/2 will be twice as longer as in 4/4. To graphically represent this, see the following two examples.

4/4         Count 1  2  3  4

4/2         Count 1      2       3        4

They are much more spaced out in 4/2. Where as in 4/8 there will be four 8th notes therefore the count will be twice as fast than 4/4.

4/4         Count 1  2  3  4

4/8         Count 1234

Same is true for 3/2. 3/8 and 2/2, 2/8.

The bottom line about simple meters is that 1. You can feel each beat separately and 2. the way we count the beat and the way we feel the beat are the same. Any meter that starts with 2.3 or 4 are simple meters.

Compound meter:

A meter is called compound when its counted in a certain way but felt differently. When how it is counted and how the beats are felt seem different, we call that a compound meter. 6/8 is often taken as an example to demonstrate what happens in a compound meter.

Technically, 6/8 means there are 6 counts per bar and each of them are 8th notes, so 6 eighth notes. It will be counted as the following:

6/8  Count 1 2 3 4 5 6

However, when you play this, you will realise that it doesn’t feel like 6 straight counts rather the groove will feel as following

6/8   Groove 1 2 3 1 2 3

It will feel like two groups of 3 beats as opposed to one large group of 6 beats. Because of this subdivision within the group that one can feel, these meters are called compound meters.

So on the same note, a 12/8 will not feel like 12 straight 8th notes per bar. Rather it will feel like the following

12/8  Count      1 2 3 4 5 6 7 8 9 0 11 12

12/8  Groove    1 2 3 1 2 3 1 2 3 1 2 3

It will feel like 4 triplets. What about a 9/8 meter? What do you think it should feel like?