Doc,

Can *any* sound cleaning program of any price range take out noise without
affecting anything else in the sound?

I've never tried the really expensive programs or devices, but I've tried
several of the affordable ones. As far as I know they all work on the same
basic principle - a many-band noise gate with the threshold set
automatically to just above the residual noise level in each band. So I
can't see how a $5,000 program will do appreciably better than a $100
program. Since they all basically notch out extremely narrow bands, they all
give a swishy flanging effect sound when applied is substantial amounts.

That said, the instructions that come with Sonic Foundry's NR plug-in, which
is what I use, say that for minimum artifacts you should do a few passes
with less reduction each, versus one pass with a lot of reduction. I have
found this to be good advice.

--Ethan