Aphex Twin Spectralised

Heres a link to an essay on images in the spectrum of some artists music

sound lab @ princeton

I recommend that you take a look at the Princeton Sound Lab at the University of Princeton.
There are lots of resources, and a special section in "software", all free and some of them open source. It´s really worth taking a look.

One of the interesting things I´ve found is PLOrk (The Princeton Laptop Orchestra).