I don't understand time signatures

There's 13 8th notes. Literally brain-dead retarded simple

It's just the beats per measure.

As for how to figure out what's a measure and what isn't purely by listening, you just kind of have to infer it. It's often quite obvious. When it isn't, people may disagree on the correct time signature for a song. Some musicians with no formal training will kind of use certain time signatures without realizing it, or use a very unconventional, asymmetric system (like a pattern of 3/4 followed by 12/4 followed by 11/4 that repeats twice, then another sequence with different signatures, then back to the original, or whatever).

For example, in the 1940s, the blind, homeless musician Moondog famously naturally formed his own time-keeping intuition which he called "snaketime". (He describes it as particularly constituting variations between 5/4 and 7/4, among other things.) An example: youtube.com/watch?v=9bcbIlE6D1A

For "snaketimey" type music, don't fret too much about deciding on an exact time signature. Just try to interpret the feel of it and break it apart however you think is closest to the original song and intention.

there's 27 quarter-whole 17th notes per every 13 bars. when you hear the trumpet go 'BLAP' you hit the fire alarm and jump out of the nearest window wearing only a pair of hockey pads. Remember to put mustard on your bagel and you'll be fine.

>makes a monotonous 13-count beat because they dont understand stressed or unstressed beats