Hi,
I remember
years ago when I used the windows sample editor "sound
forge", that it had a pretty good noise removal feature. You could
provide a sample of only noise and have it analyze this for even better
removal.
While I'm sure those who know and use Ardour will tell you Ardour
can do
it (and how to do it) ...
Well, I am that "Ardour is best"-type and I must say: as of now
Ardour
is not the app for removal of a continual noise like hiss. It can be
used for the removal of crackles and the like but not for hiss or hum.
As it is a pure realtime-app it is not designed for
offline-analysis/recalculation jobs.
Bummer, I'd have thought Ardour could do it. I've never thought of
Ardour (or any DAW software) as a "pure realtime-app". But I don't know
Ardour.
What comes to my mind (I only used it once though) is Gnome Wave
Cleaner:
http://gwc.sourceforge.net/ already mentioned in the past on
this lits. It even has a gui!
http://gwc.sourceforge.net/
I thought that, although pretty old (last software update 2003?) and
aimed at something different (old LPs), I'd mention Gramofile which also
did some kind of noise (hiss, crackle etc.) reduction (no gui but quite
easy to use). I used it about 4/5 years ago and didn't seem bad (your
mileage may vary).
http://www.opensourcepartners.nl/~costar/gramofile/
Good luck,
Lorenzo.