I'm just reading about hybrid meters: which combine simple time and compound time.
It seems to me that the time signature 9/8 can have two possible (yet distinct) meanings.
One possibility is that it could represent compound time, with three beats per measure, with a dotted quarter note having one beat.
Another possibility is that it could represent hybrid quadruple time, which would have four beats per measure, with one of the beats containing 3 pulses and the others containing two pulses.
Are these two time signatures related somehow? or are they completely distinct, with the accompanying score being the only clue to figuring out which one you're dealing with?