Specific time - compound time signatures
The bottom number represents the note value of the subdivisions of the basic pulse of the music (in this case the 8 represents the quaver or eighth-note) the top number indicates how many of these subdivisions appear in each measure
Usually each beat is composed of three subdivisions
To drive the unit of the basic pulse in compound meters double this value and add a dot and divide the top number by 3 to determine how many of these pulses there are each measure
This example announces that each measure is the equivalent length of two dotted crotchets (dotted quarter-notes) you would pronounce this as six-eight time
Common time
This symbol represents 4/4 time
It derives from the broken circle that represents imperfect duple meter in fourteenth-century mensural time signatures
Alla breve or cut time
This symbol represents 2/2 time indicating two minim (or half-note) beats per measure
Here a crotchet (or quarter note ) would get half a beat