I am now doing Bach's invention no 12 - which I love,
What my teacher wants me to do is two notes in the trill to match one in the right hand (until I can get to the point of freeing it up). This I can do at a lugubriously slow speed! It is accurate but sounds awful.
As soon as I begin to speed up, my hands get out of sync (yet I don't have any problem the other way round, with right hand doing the trill to the single notes of the left hand, whether fast or slow). As I am at the polishing stage with this piece I have been increasing the speed, one notch per day, on the metronome. I start each day with scales and Hanon in the 'new' speed. I then do each hand separately until I can do each well at the new speed. And I can do the left hand trill like this - I can do the speed required so long as there is no distraction. I then try both hands together all the way through so that I can identify the parts that need special attention and each time it is the left hand trill. So I go back to slower but never get the two together at a reasonable speed. As my hands can do it, I think it must be something in my head, and wonder if there are any other ways of thinking about it that will make it click.
I do feel that something clicked with the right hand and like riding a bike, I don't think I will forget it but as I don't know what or how I don't know how to do the same thing with the left hand.
I'd be grateful for any tips.

