system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: the difference in time signatures, including the more complex (to me) ones used in jazz, like 6/8, 7/4, etc.

i have yet to find an explanation that can change the only example i’ve ever known which is 4/4. is it just how many notes can fit into a bar? why can’t the bars just be made longer? don’t all notes and bars have to eventually come back to an even number, like in 4/4? 12 is all i can thing about...
gpt
The bottom number indicates which type of note is a *beat*. Quarter notes (4), eighth notes (8), etc.

The top number indicates how many beats per measure.

So 6/8 says that eighth notes are a beat and there will be 6 beats per measure.

7/4 says that quarter notes are a beat and there will be 7 beats per measure.