What is compound time and what is the difference between it and simple time?

Answer 1

Most regular musical meters are either simple or compound meters. The term "simple" and "compound" refer to the natural divisions of the pulse within each measure.

In simple time, the pulse divides into two equal halves. Most music shows this by using quavers that divide into semi-quavers (or, quarter notes dividing into eighth notes). One would count the rhythm as 1 & 2 & 3 & 4 &. Simple time can consist of two, three, or four pulses (ie. 2/4, 3/4, or 4/4 time). In all cases, each main pulse or beat of each measure would naturally divide into two sub-pulses.

In compound time, the pulse divides into three equal portions. Most music shows this by writing each pulse as a dotted quaver (or dotted quarter note). Each dotted quaver divides into three equal semi-quavers, counted as 1 & a 2 & a.

Compound time can consist of two, three, or four pulses. These time signatures are written as 6/8, 9/8 or 12/8. In all cases of compound meter, the top number is a multiple of 3, because the number represents the number of groupings of 3 (6 = 2 groups of 3, 9 = 3 groups of 3, 12 = 4 groups of 3).

Answer 2

Compound time is a metre in which each beat is divisible by three (e.g. 6/8), as opposed to simple metre.