For some background, I played percussion in marching band in HS and had classical training on clarinet up through college. I know how to count complex patterns but have always found a problem actually doing it on syncopated 16th note patterns (particularly with ties and 16th rests) when the tempo is fast. This has reared its ugly head recently again whilst trying to work through book 3 of the Hal Leonard Bass Method and trying to learn faster rock/alt/punk songs. The trouble is I can’t mentally “keep up” with the counting at faster tempos and resort to just playing by ear/feel. I always learn songs/pieces by slowing them way down and building up speed, but when I get to over 90 bpm, counting out the "one-e-and-a"s just go by too quickly for me. I wind up paying more attention to the count and then am “behind” in the actual playing. Any tips on this? Does it really “matter” if I can’t keep up mathematically counting if I ultimately get it “right” by ear?
Don’t worry too much about it. As a trained musician, you already know that the key to learning a part is to slow it down until its notes/timing/phrasing are engrained in your fingers. That’s the most important piece of the puzzle.
The next thing to do is to apply what you have engrained to the backing track. As with the first step, it is key to sloooooooow that puppy down while you play along at your currently comfortable tempo.
The next thing to try is to gradually speed up the backing track until you hit a wall as you play along to it. Then slow the track back down until you don’t. Rinse and repeat until you’re playing up to the tune’s tempo.
The dichotomy of learning to play a musical instrument is that it requires practice to the point of tedium, because “effortless” playing can only happen once the time and effort has been put in.
In other words, you gotta pay your dues if you want to play the blues (or any genre!).
So, I would call that “fudging it” and, in my book, that is quite OK as long as it is “musical” (and it would be your personal definition of what that means). A problem arises though once you need to align to a) a drummer, who perhaps plays a similar rhythm or plays in the “holes” of your rhythm, or b) another instrument playing your lines in unison. Then, of course, you either both stick to the “mathematical counting” or “fudge” it in exactly the same way.
I have found Saher Galt’s videos really good in getting better at decoding rhythms, to the point where you know how it’s played without having to really count it (if that makes any sense):
The video does not work (at least in Germany). Just another copyright issue? Because I need it 
We have lift-off! 
Mike’s advice is solid.
- Slow it down
- Listen and emulate - get it under your fingers. Get the “feel”.
Now it’s much easier to figure out the counting.
Next, speed up the counting.
I struggle with that also (song is faster than I can count in my head). I slow it down like @MikeC said to internalize the timing, and eventually the beat is internalized and I dont have to count. Most likely I will never be able to count faster, so this will have to do.
But eventually the speed exceeds my ability to verbalize the count in my head…its not just a matter of PLAYING up to speed…its that i can’t count 1 e & a; 2 e & a, etc. fast enough
Then it’s the Reggae life for you 
except i like ska-punk!
The point is: Once you have the essence of the tune under your fingers and between your ears, you can play it without counting.
It’s not about “1-2-3-4,” it’s about making music.
Counting is equivalent to training wheels on a bike: Once you are comfortable pedaling while maintaining your balance AND steering, you’re no longer just operating a machine, you’re actually going somewhere. It’s an experience.
The same analogy holds true for manipulating the physical and intellectual machinations of playing an instrument: Once you have the motor skills and the feel (timing/phrasing) of the tune in your head/heart, you’re beyond making sounds — you’re playing music.
I barely ever count when I play, and only do so when I absolutely have to. It just doesn’t feel necessary most of the time and it hasn’t really limited my ability to play anything. Just feel it
I only do it while learning a song, or if there are no drums. But usually I’ll add a drum track for lead-ins and such and then delete it later.
This is a great analogy. I only count when I’m learning new song’s difficult parts. Usually, it’s the pickup note(s) and some funky ghost notes. I’m working on the 7/8 song right now, it’s not difficult but it’s not a walk in the park either. When playing at original tempo finding 1 is not too bad but when I slow it down to get the correct articulations counting gets tricky.
I like Anika Niles, but doing math with her music is not fun sometimes, 
Same goes with Simon Phillips but at least he loves to disguise his songs odd time in 4/4 it’s more approachable.
Awesome drummer - love her music 
A few songs on her first album change time signature about 3-4 times, lol. I messed around with that for a spell but it’s not an easy thing to do.
You’ve seen this, right!?
Oh yeah! I saw that. That’s awesome.
Speaking of German this is definitely my favorite drummer from Drum tec Ralf Schumacher. This one has a couple of tasty bass as well.
