Once I got the controls down this was really fun to play! Making this epic sounding chorus (requiem) and letting me decide how long to hold each note for made me keep playing. I loved the audio, you did a really good job on that this whole game wouldn't have worked without it.
What it needs is a tutorial. I had duplicated the tab so I can have the controls on one monitor and the game on the other to see what I was doing, and I'm still not quite sure how score is given. The green bar and red bar seemed to fill up kind of randomly. I don't know how to harmonize, but it was fun to experiment with the different key combinations.
Good job!