Hello Carel and Hemert,
Trying to hear and recreate the music with the instruments is cool, I liked that.
It's a little difficult to hear the song because it only plays for a few seconds when you hit the note. I don't know if the standard sound of the stage was supposed to be a metronome, but regardless, it ended up getting in my way a little when trying to hear the music and tuning.
I enjoyed the art, music and history as well. With a little polishing it can become something really cool. Nice job!