Interesting concept.
I'd also recommend having the notes on the keyboard instead. Comfiness aside, it would allow you to use chords.
Plus, I find the appearance of each passage a bit too sudden, and having 3 different points on the screen to check feels a bit clunky. An alternative would be having the turning signs line up with a see-through display/frame on each side, and making the player to input the correct note(s) as they line up with the frame. They would still need to time the inputs well, but with a bit more easier (and a lot more "diegetic?") interface to work with.
Cheers!