Hi John. Sorry for missing this earlier.
Are you sure you’re really synchronizing at the faster speeds? What I mean by this, is just that when you go fast, you’re on autopilot and it’s tough to really know what’s going on. Things can feel one way and totally be another way. Have you filmed yourself close up to see what it looks like? Is the intended pickstroke really hitting the note you’re fretting at the right time?
For example, say we’re talking about shreddy type speeds like 180 and above sixteenths, and you’re doing something simplified like a pattern that repeats on a single string. You can sometimes find that if you start out with the downstroke on a particular note, it will drift to where it’s upstroke by the end of a few repetitions. It may still sound clean, but something wasn’t locked and one extra pickstroke threw the whole thing off. It can be very hard to feel that this happening. Filming yourself is a good way to verify. This way you can eliminate whether it’s a picking issue at all.
Re: very slow speeds like 120bpm and below, I don’t even know if that being “synchronized” really means what it means at the higher speeds. Those speeds are slow enough you can almost consciously anticipate what is coming. With alternate picking, your picking hand is only moving half that fast and that may simply not be fast enough to require the same kind of chunking that goes on at the higher, “autopilot” type speeds.
With synchronization in general, chunking is the answer. You can be heavy handed about it and actually place bigger accented pickstrokes on the first note of repeating sequences. In the “Starting With Speed” chapter, at the very beginning, I included two clips of a single note played with different accents. No or very little accent in groups of fours, and then strong accents on sextuplets. This is actually pretty tricky to do. I never actually practiced hands separately like this when I was first working out hand synchronization years ago. I found it much simpler to do repeating patterns that involved a distinct fretted note on every pickstroke. The Yngwie six-note pattern was a go-to for this, as was the Di Meola sixes, i.e. three contiguous diatonic notes descending or ascending, played twice in a single position.
Anyway I can do the single note chunking now even with no fretting hand, and it’s interesting that if I think about it too much, it breaks. To do the sextuplets with no left hand, I actively have to “not” pay attention, and just feel the force of the accent and nothing else. Then it comes out nice and tight. It’s clearly just a memorized sequence of movements that doesn’t want to be messed with.
If you haven’t tried this type of single-string chunking, either with or without fretting hands, I’d recommend giving it a shot. Once I had it faster speeds with accents, there was no issue slowing it down to medium-fast speeds around 150. None that I can remember anyway.
If you’ve already done this, and you’ve verified with video and it’s working at the higher speeds, try slowing it down to your grey zone and see if the accents are still there. You will actually be able to see them because they are larger pickstrokes. If they are still there, then perhaps it’s not a picking hand issue. Try different left hand patterns with different fingerings and see if it’s still there. If it’s present on some patterns and not others, then it may be related to specific fingers.
Anyway, test and test again. If something isn’t working, devise a test for it that can rule out one or more causes.
for what ever bizarre reason though when I’m playing at ridiculously fast speeds like 150-160 in double time things seemed to be synced up better. My hands just start getting fatigued or I’d keep doing it. I’d love to hear Troys take on these Grey areas because those are nice tempos to play in and are more common in most rock songs. 