For example, why would someone choose 2/2 time over 4/4 time? It will still give your 4 quarter notes per measure, just at half the time spent on each quarter note.
pdpi: Played at the same speed, the difference is in the accent — that is, where you put more emphasis.
Listen to Sousa’s [Fairest of the Fair](https://www.youtube.com/watch?v=pr0ZI3j-fT8). As soon as the drums kick in, you should be able to get a really strong “one, two. one, two.” sort of feel. That’s what 2/2 or 2/4 sounds like.
Now pay attention to the bass line for Queen’s [Crazy Little Thing Called Love](https://www.youtube.com/watch?v=zO6D_BAuYCI). That’s a “one two three four” feel. That’s your 4/4.
Let’s try the ones that are multiples of three now. 3/4 vs 6/8 is the difference between “One and Two and Three and One and Two and Three and (…)” for 3/4, and “One and a Two and a One and a Two and a (…)” for 6/8: one has three beats that divide into two halves, the other has two beats that divide into thirds. You can hear this difference in Bernstein’s [America](https://www.youtube.com/watch?v=Qy6wo2wpT2k) from West Side Story: The bit that goes “*I* like to *live* in A-*me*-*ri*-*ca*”. Note how The first half has two accents (“I” and “live”) and is in 6/8, and the second half is 3/4 with emphasis on “me”, “ri”, “ca”.
Galuvian: Its not always about the ratio, its mostly about where you want the emphasis to be and how fast that beat goes. Also keep in mind that in many 20th century arrangements composers will stick in measures with different time signatures to produce a certain effect, and those measures don’t always behave the same as if an entire piece were written in that meter.
Some time signatures are close to interchangeable. 2/4 is often really similar to 2/2 or “cut” time even though those aren’t the same ratio as 2/4. Having the beats on quarter notes is a little easier to read for some musicians that haven’t played a lot of the old marches written in cut time.
Others are not. 3/4 is 3 beats per measure, each beat being subdivided into 2, while 6/8 is 2 beats subdivided into 3.
6/4 can mean a few things. If an entire piece is written in 6/4, it probably is in a slow 3. But if a random measure is in a piece, it may just represent a 4/4 + a 2/4 measure to extend a phrase by a couple of beats.
In addition to 2 vs 3 feel, the composer arranger will take other things into account, like how much work would the conductor be doing, and how much effort is to write everything out. Going back to 2/4 vs cut time, the advantage of 2/2 is that really fast notes can be written as 16th notes instead of 32nd notes. That makes it easier to read and easier to write.
SausageSmausage: 2/2 time and 4/4 time are actually very different. 2/2 songs are usually a bit faster, vs 4/4 time which is very standard and can go all over the place. You usually only see 2/2 time in marches, to keep time with feet while marching.
Ansa88: It has more to do with the way the song is written rather than played. If you want something looser that you can experiment with, you have a time signature that you can fit more notes into. If you want something to have a more rigid structure, then the time signature that you can fit less notes per measure into will work.
thackerh: “For example, why would someone choose 2/2 time over 4/4 time? It will still give your 4 quarter notes per measure, just at half the time spent on each quarter note. ”
In 2/2 time, you would not have 4 quarter notes per measure. You’d have 2 beats in a measure, and the half note is the “beat.”
The top number in the ratio is the number of beats per measure, and the bottom number is which note value constitutes one beat.
Pinwurm: The top number is the beat. The second number is how-many-beats in a bar.
In 2/2, there are 2 half notes per measure, which means it’s *like* 4/4, but often’s faster. The beats are counted by the half note instead of the quarter note
You can certainly transcribe 4/4 music as 2/2 and vice-versa, it really depends on the composer and how they view their work. Think of it like paintings. Some painters work with *large* canvases – others work small. Large paintings can be more detailed – but may take longer to create, study and analyse. Small ones can be less detailed, but easier for the viewer to take in.