That seems surprising. It's not like there's a discrete threshold between "able" and "too fast". I'm not a violin player, but just about anything I can play slo

That seems surprising. It's not like there's a discrete threshold between "able" and "too fast". I'm not a violin player, but just about anything I can play slowly on a bass or piano, I can also play quickly, given enough practice, even if it means I can only initially play it at quarter or third speed with a metronome. Aside from some virtuouso performances, I think any beginner/intermediate player with a decent ear and headphones/sheet can play any piece at quarter speed. It seems like muscle memory is one of those things you really can achieve through mindless repitition with good technique, while theory requires a lot more focused practice. edit: Okay, disregard that, the above comment is completely different and I guess I agree now.