
A book I thought was great has no code in it, but is FULL of very useful info about audio and computing it. Computer Music by Dodge and Jerse, ISBN 0028646827 (1997) ... a little pricey, might be hard to find, but very hard to beat.
[1] I haven't seen Richard's book (I'm sure it's great - and I will see it, thanks for the tip) ... he just might be pitching this idea in there!
[0] https://archive.org/details/onsensationsofto00helmrich
Sethares sounds familiar. A key modern classic is 1985 Charles Dodge, Thomas A. Jerse: "Computer Music : synthesis, composition, and performance". A pricey book new (worth it!) it digs into everything from the basics to the advanced. You will not exhaust it!
Surprised but, for a limited set of users, this puppy can be accessed online. See the link for the list of topics. [1]
[1] https://archive.org/details/computermusicsyn0000dodg
An alternative to the computer is to take a little recorder with a good mike out into the wild and record, the rocks, the insects, the trees, the plants.... and water, the greatest improviser!
[3] http://chuck.cs.princeton.edu
[4] http://supercollider.sourceforge.net
[5] http://www.amazon.com/Computer-Music-Synthesis-Composition-P...