when youre listening to a song, how can you figure out the correct tiem signature..

like i listen to a lot of progressive so thats a bunch of irregular time signatures

example: whats the difference between 14/8 time sig and 7/4??

14/8 means there are 14 notes in a measure, and that an eighth note is one beat.
7/4 means there are 7 notes in a measure, and that a quarter note is one beat.

The only difference should be how you would write everything down. As far as I know, they would both sound exactly the same. I'm not expert in time signatures, and I've never felt compelled to use such strange timings, but as far as I know they're basically the same.

The odd time signatures can be figured out, 2/4, 4/4, 8/6, 8/12 are hard to tell because you can technically count all of them in 4. The snare drum usually has the 1,2,3,4 beat or the 1 and 2 and beats. For 3/4, 6/4 beats you can usually hear a triplet feel in the bass drum.