This is a really neat application! Since seeing the fourier image analysis on HN a couple days ago, I've been looking into in-browser DSP.
On my laptop it felt pretty responsive, but I notice that you have a disclaimer not to sing a note faster than 80bpm. Is that a limitation of browser processing power?
Also, I'm curious what you thought of VexFlow? Were there any drawbacks you noted when using it to render notes, and did it play well with angular?