There is a relevant question on Math.SE: [Mathematics and Music - reference request](https://math.stackexchange.com/questions/79885/mathematics-and-music). I can second the top-voted answer there, which suggests the book [*Music: a Mathematical Offering* by Dave Benson](https://homepages.abdn.ac.uk/d.j.benson/pages/html/maths-music.html).