I realize the question may sound too broad or unclear but specifically, I was recently thinking that you could take a certain genre of music, or a certain composers' works, and mathematically define the reoccuring patterns within the music. For example, I appreciate Steve Reich’s ability to incorporate math into music. You hear just a few notes but it is still a very complex equation. He invokes this sense of floating in a vast sea of numbers, (for me), in a very fluid linear system of playing. His goal seems to be creating a sonic architecture and math as music. Those same experiments in sound, if applied in a visual sense could be turned into plans for extravagant buildings... right?
Yes! What I find fascinating is you can find mathematical thinking is many different music styles.
Two books that examine 'classical' style:
The Math Behind the Music (Outlooks) by Leon Harkleroad Link: http://amzn.com/0521009359
A Geometry of Music: Harmony and Counterpoint in the Extended Common Practice (Oxford Studies in Music Theory) by Dmitri Tymoczko Link: http://amzn.com/0195336674
You may want to look into the music and theoretical writings of George Perle. Generally the search fro patterns in music is going to be style specific so it depends what style you're talking about. It's also difficult because repetition in music isn't always exact so it can be difficult to quantify. In earlier classical musical styles you could look into Robert Gjerdingen's book "Music in the Galant Style" which talks about commonplace patterns in classical music, but is not very mathematical in its approach.