This is the Audacity Noise Reduction Code. 

It was taken from this copy: https://github.com/tals/audacity-noise-reduction/tree/master/noisereduction

The copyright within that code reads: 

  Audacity: A Digital Audio Editor
  NoiseReduction.cpp
  Dominic Mazzoni
  detailed rewriting by
  Paul Licameli

I believe it is licensed as GNU/GPU
