Very cool concept! And pretty good execution! I'm positive my heart rate just went up quite a bit.
Regarding controls, the A/Z key was pretty obscure, which let to weird hand placement. I found out the mouse left click worked better for me. Speaking of the mouse, did you guys consider using it to guide the character rather than WASD? It is usually more natural and therefore easier in situations like the "double bass ring" that happens soon after the tune starts.
One last thing regarding gameplay is that sometimes there's an easy way out in just standing there. If done right you end up avoiding most projectiles and you only have to move slowly to keep up with the slow spinning (btw I didn't get too far but I suppose the disc rotation speed increases with time/difficulty?)
A solution to get rid of the "lazy approach" is to apply a constant forward motion to the character. Kinda like a snake game or the recent slither.io. This forces interaction by forbidding a static player. Of course it requires a different approach in level design.
The music itself was great with very distinct elements reflected in the (fitting) graphics. Maybe I would have modelled the enemies like oscillating soundwaves instead (sine, square, saw).
I really liked the minimalism and the entire game happening in just one speaker cone. Its round shape makes this whole thing pretty tricky! :)
I hope you had fun making it! It sure is fun to play! (Giving you verbose feedback here but the note I gave is very good!)
See you in the next one! Take care!