As a long confirmed musical mathematician (or is that a mathematical musician?) there is a lot to interest me in this article from Plus + magazine, which is Cambridge University's internet magazine "which aims to introduce readers to the beauty and the practical applications of mathematics".
This fascinating article explains how pitch works (pitch being how high or low a note is), why octaves (notes considered to be an eighth apart) sound pleasing, why certain notes sound well together, or conversely, why certain notes are dissonant, why harmony (notes playing together) requires the third of the chord (that's right you Grade 6+ music theorists!) and what different keys are based on.
For further reading in this area, I can strongly recommend John Powell's book - How Music Works. He is coming at the subject of music from a Physics perspective. If you take nothing else from this book, it should be that Perfect Pitch is learned! And not some incredible innate ability bestowed upon the blessed!
There are LOTS of other books in this area and I would love to hear about your favourites in the comments or by email. I would also be extremely interested to hear of any links between music and whatever your other favourite subject might be!