*Subdivision of the Beat:
A simple time signature subdivides each beat into two parts. It is also possible to have a time signature where each beat is subdivided into three parts. These are known as compound time signatures. 6/8, 9/8, and 12/16 are examples of compound time signatures.
*What the Numbers Mean:
In a simple time signature, the top number gives the number of beats per measure, while the bottom number tells you which kind of note gets the beat. Compound time signatures don't work this way. The meaning of the numbers in a compound time signature are explained below.
*The Top Number:
The top number represents the number of subdivisions in a measure. For example, if the subdivision is an eighth note and the top number is six, there would be six eighth notes per measure. Don't confuse this with the beat. The top number in a compound time signature must be divided by three in order to determine the number of beats per measure. Dividing the '6' in 6/8 by three equals two. This means that there are two beats in each measure of 6/8.
*The Bottom Number:
The bottom number represents the note value that subdivides each beat. This number can be used to determine the kind of note that gets the beat by adding three notes of this value together. The resulting note will always be a dotted note of some kind. For example, the bottom number in 6/8 time is '8', which represents an eighth note. If you add three eighth notes together, they equal a dotted quarter note. The dotted quarter note is the note that gets the beat in a measure of 6/8 time. 6/8 means that there are two beats per measure with the dotted quarter note getting the beat.