[QUOTE=Kevbo]
Finally, to really screw things up, it is VERY common for musicians to count tunes written in 6/8, 9/8, and 12/8 tunes as having 2,3,or 4 beats per measure. An irish jig in 6/8, for example, would require counting at around 360 beats/minute (6 per second) if you stuck to the time signiture as written. Instead, you change it to a 2 count, at ~120 beats/minute. Each beat then gets 3 eighth notes or the equivilent. This is known as “compound time”.
[/QUOTE]
Kevbo’s got it. Here’s a post I wrote about this from this thread a few years ago:
[QUOTE=Moe]
Actually there is a bit of a misconception about the bottom number. The buttom number is determined by the way the beat is subdivided. If the subdivisions are duple the bottom number is 4 and if they are triple it’s 8.
4/4 is counted: 1 & 2 & 3 & 4 &
(the 3 tends to be stronger than 2 and 4 but weaker than 1).
3/4 is counted: 1 & 2 & 3 &
In the first case there are 4 beats in each measure (cycle) and in the second there are 3 and each are divided in half (or multiples of 2). A quarter note represents one beat of time and quite nicely divides into 2 eighth notes. Want 4 subdivisions? We have 16th notes for just that purpose.
But say you wanted to divide the beats into 3 equal parts? To represent that on paper you need a note that can represent a third of a beat. Well, there really isn’t a note that does that exactly. The best they’ve come up with is to use 3 eighth notes and then a bracket joining them with a little “3” above it to let you know that they are triplets. That works fine if you need it here and there, but if the entire piece has a triplet feel all those brackets will get quite distracting very quickly.
The solution is to simply count the triplets as ordinary 8th notes. Afterall, it is pretty arbitrary what you actually call the notes. By putting an 8 on the bottom of the time sig, it tells us to count each measure according to it’s 8th notes. It does NOT, however, mean that the 8th notes are the beats. In fact the beat is actually moving in dotted quarter notes (a dotted quarter = 3 eighth notes). Hence:
6/8 is counted: 1 2 3 4 5 6
There are 2 beats and each are divided into 3. Likewise 9/8 has 3 beats and 12/8 has 4, the first beat always being stronger than the others.
Let me see if I can think of some popular examples. Everyone knows the Beatles, right?
The Sgt. Pepper reprise opens up with a solo drum intro in a very clear 4/4, with the duple subdivision explicitly stated by the bass drum on beat 3. i.e. 1 2 3 & 4
Now take Norweigen Wood. You could count it in 4/4:
I once had a girl or should I say she once had me?
1 2 3 4 1 2 3 4
But it’s much more descriptive of the rhythmic feel if you account for the triple subdivisions inherent in the music and particularly the vocal/sitar melody:
I once had a girl or should I say she once had me?
**1** 2 3 **4** 5 6 **7** 8 9 **10** 11 12 **1** 2 3 **4** 5 6 **7** 8 9 **10** 11 12
Thus it is in 12/8 by my count.
(That was a coding nightmare).
[/QUOTE]