Hi,
There is an immense world of audio software that is sometimes hard to find. So here, I will give a short list of beginnings of paths to that software. Some of it is for MacOSX, some of it is for Unix and can be and has been compiled for OSX, and some of it is currently MacOSX specific but will one day be OSX runnable.
www.csounds.com
CSound -- a really low level generator-based audio application. Programming interface -- not for the faint of heart.
www.reckankomplex.com
This is not a software application but a forum of a really amazing TiBook/Experimental/Electronica composer in Boston. If you go to his forums, you will find threads that put you on the sound software path. Especially, find links to backtobasics, spongefork, soundhack, and other essential Mac sound gadgets. Truly amazing stuff.
www.tcworks.com
Spark* -- Sound recording and editing software brought natively to Mac OSX early in the game. I believe the higher level version supports VST to some extent.
www.cycling74.com
MAX/MSP - another generator-based environment for sound unit production. Excellent for live performance, excellent for learning about sound programming. Like buzz for the PC, or CPS for the PC, only way better, IMHO. Check it out: it is a whole world to get lost in.
www.hitsquad.com/smm
A repository for all kinds of sound software.
There's more, way more, out there. But these links will get you on the trail. Best of luck,
-ZeroAltitude
