In the stave above there are two 4s. This combination is known as the 'Time signature' of the music.
The top number
The top '4' tells us there are four beats in each bar. We could put 3 or 5 or any number we can think of, but typically this number is a 2, 3 or 4.
We refer to the time signature as 4/4(four-four) or 3/4(three-four) where the top number comes first.
Here are some more examples:-
|3 beats per bar||2 beats per bar||5 beats per bar|
|Each beat is a crotchet|
|Three-four time||Two-four time||Five-four time|
The bottom number
The bottom '4': it says that these beats are crotchets.
If the number were a '2' then these beats would be minims. Similiarly, if it were '8' then the beats would be quavers.
2, 4 and 8 are the only numbers normally encountered.
|3 beats per bar||3 beats per bar||3 beats per bar|
|Each beat is a minim||Each beat is a crotchet||Each beat is a quaver|
|Three-two time||Three-four time||Three-eight time|
Special time signatures
There are two time signatures that are not in this format:
|4 beats per bar||2 beats per bar|
|Each beat is a crotchet||Each beat is a minim|
The same as 4/4 also known as common time
|The same as 2/2 also known as Alla Breve|
There are some special considerations with Compound time which are dealt with separately.