In the lesson video there is good explanations on different meters.
What I do not get is how is numbers in time signature defined? Understanding this could help me remember the time signature markings for different meters.
4/4 is logical as its simple, four beats per measure. But beats in others do not add up to me. 3/4 is tree beats per measure but where does the 4 come from? Like why is compound meter with three beats dividing each to three sub-beats marked as 9/8?
At it’s most basic, the bottom number is the standard beat unit, the thing which dictates the pulse. 4 means quarter note pulse.
The top unit is the total number of beats in a measure.
So 4/4 means there are 4 quarter note beats in a measure.
3/4 means there are 3 quarter note beats.
Things can get slightly more complicated in compound meter. For instance, 6/8 means there are six 8th notes in a measure, but the pulse groups 3 of those.
Here is a good resource to get the sound of each meter in your ear.