Excerpts from Malte Steiner's message of 2011-02-07 23:04:27 +0100:
I second SND which seems to be the editor but it comes
with a learncurve.
Other candidates for extreme sound processing are Csound and Pure Data,
they even let you create your own processing patches.
Cheers,
Malte
SND seems to be extremely powerful and flexible but its learning curve
is insane. I just found out that it has a built-in extensive,
half-working, possibly useful help system.
There's SND-ls that aims to make SND usable by mere mortals, but I'm not
sure it achieved this goal yet:
http://archive.notam02.no/arkiv/src/snd-ls/