A quick scan didn't reveal to me whether he's time aligning the signals during the subtraction. I've played with listening to the wav-mp3 signal before, and I seem to recall that the mp3 encoder would introduce a little delay.
I added a transient pulse in front of the music so that I could (visually) time align the signals before subtracting them.
I added a transient pulse in front of the music so that I could (visually) time align the signals before subtracting them.