Fantastic little puzzle game. Its interesting to see a music-based puzzle game that has nothing to do with hitting beats in time. Took me a moment to understand the core mechanic, but once I did, I managed to get through the rest of the game, only struggling a little bit, and thats because I'm bad at puzzle games.
I think it succeeded with what you were aiming to do, and did it really well and kept on the theme, however I believe the game could do with a more in depth tutorial to help explain the central mechanic.
The only thing I would suggest adding is the ability to replay the tune without needing to take a guess, as that would really cut down on idle time which you can experience just because you're thinking about the solution too hard, and forget the tune.
Great game, would absolutely play a full release