What is a time signature?
If you look at a piece of music you will notice that at the beginning there are some numbers which sit on top of each other. This is a time signature, and tells the reader how many beats per bar there are.
But what does the 4/4 mean exactly?
The top number tells us how many beats there are per bar, and the bottom numbers tells us what note values to use for these beats. So for a 4/4 time signature the top number means that there are 4 beats per bar, and the bottom number indicates that we are using crotchets for each beat. So when you see that the bottom number is a 4, this tells us that we are using crotchets for each beat.
A 2/4 time signature for example tells us that there are 2 crotchet beats per bar. The 4 at the bottom indicates crotchets like before, but this time there are only 2 crotchet beats per bar (the top number). A 3/4 works exactly the same, so the 4 at the bottom again indicates crotchets, and the 3 at the top tells us that there are 3 crotchets per bar.
You don’t however have to always write music using crotchets as your beats per bar, and it’s very common to use quavers as well. Time signatures using quavers are written with an 8 at the bottom rather than a 4. So this means that in a 3/8 time signature we are going to play 3 quavers per bar. Another common quaver time is the 6/8 time signature, which means we are playing 6 quavers per bar (also 9/8 and 12/8 are very common).
Finally, you may also see the 4/4 time written as a C, which looks like this:
This is called common time (and also imperfect time) because the 4/4 time signature is so popular. However the C doesn’t stand for the word ‘common’ and is just a coincidence. This symbol is actually derived from a broken circle which was used in music notation between the 14th and 16th centuries. A full circle today would have represented the 3/4 time, and was called tempus perfectum (perfect time). This is why the broken circle is also sometimes called imperfect time.