Audio noise reduction: how does audacity compare to other options?
I am the author of the code you are reading.  It appears you were an alpha user of Audacity 2.1.0 in advance of its release, which was only days ago.  You have a version of the noise reduction effect with many experimental optional controls exposed to the user that are not in the release version.

You may be interested in what I wrote here about the inadequacies of the previous version of the effect that I tried to remedy with this rewrite.  But the overall procedure remains unchanged.

http://wiki.audacityteam.org/wiki/Proposal_Noise_Removal#Critique_of_current_Audacity_Noise_Removal_by_Paul_Licameli