[lunixbochs]

Maybe some kind of alignment metric, to measure how far off on timing notes tend to be?

I can also imagine a generalized "local error rate" which measures how far away errors tend to be from each other. If errors tend to be clustered, I would guess that's showing inability to follow some musical pattern. I think you'd want errors to appear randomly distributed rather than clustered. (This metric might make sense for speech too)