Incredibly spectacular good game, I love the art style but I also have a chronic skill issue so I couldn't enjoy it past level 8.
maybe like a bloom pulse on the headphones that grows to full color on the beat so you can see the wind up, in a color like red/blue/green. Could change depending on the level, tempo, setting.
Such a sick game btw, really cool stuff.
You should consider a steam drop with some slide notes or something, just really cool project.