Mathematics of music is a frequent guest topic of John Baez's This Weeks Finds in Mathematical Physics. Week #234 was one of the most interesting, referencing lots of work, including Tymoczko's : http://math.ucr.edu/home/baez/week234.html Many books are mentioned there already, but I would like to add one more, Benson's "Music : A Mathematical Offering", which is a little lighter read (at least not going into category theory stuff), downloadable here : http://www.maths.abdn.ac.uk/~bensondj/html/maths-music.html