This book, written in the 1970s, is a must-read for researchers and musicians interested in musical timbre. Erickson's review is excellent, with a number of references that have been subsequently ignored, much to the detriment of the research community. The later chapters on examples of timbral manipulations in composed music weren't very interesting to me, given my lack of background in modern orchestral music, but would probably be valuable to someone interested in that kind of thing.