It is great that the author included some known pieces for you to "watch" (click the music icon on the bottom right). Of course one first goes to Bach to test the mettle. While "watching" BWV 578 one thing I immediately noticed was how the rhythm of the counterpoint stood out to me in a new way. I have seen many visualizers (the great https://www.youtube.com/user/smalin/videos deserves mention), but I have found most to have some sort of constant object moving around to visualization the tones (i.e. a ball moving up and down). In this case, there is no "moving object" that we follow and we are instead left with the tones in isolation. I greatly enjoyed seeing how this increased my appreciation of Bach's rhythmic counterpoint as I could see when multiple strings were plucked at the same time with the clear purple coloring. Amazing work!