i find it very hard to find good texts about sound and music when looking in the programming area
the hardest part being "what part of it have i learnt yet?", since i have never found anything describing the part already documented against the great unknown (=things no-one has well understood yet)
from sound synthesis to automatic music classification, information is rare, and nearly impossible to easily applicate to your current needings (while you can find hundreds of step-by-step tutorials in minutes when looking for a solution to a visual processing).
i think it's time to have a bookmarks list on the subject
mine are :
www.rotorbrain.com/foote/papers/index.htm (a lot of articles about musical structure extraction, "beat spectrum" are the first words to look for)
www.fmod.org (very good sound api with great features, great documentation and active community)
www.gamedev.net/reference/programming/features/beatdetection (it seems to be the only easyily available tutorial on beat detection)
www.crca.ucsd.edu/~msp/techniques.htm ("The Theory and Technique of Electronic Music" a book about lot of stuff...)
www.mperfect.net/aiSomMusic (using self organizing maps for automatic classification of music)
feel free to share yours