Really nice. Now I know the meaning of those squiggly lines. I also like the sparse full screen layout.

A few minor things: While jumping to time points works, scrubbing does not. Instead, the notes image gets dragged. You could embed the image as a background-image instead of an <img> to prevent that. Or catch the dragstart event on it and return false (http://stackoverflow.com/questions/4211909/disable-dragging-...). A custom Rails error page or better error handling would also be nice (http://notezilla.io/bla). And there are a few console.log's left (TIME!!!! :)

Did you match the music to notes by hand?