Denoising: explanation of settings

[fwolfst]

I try to use the denoising as it gives better/different results than the audacity one.
As a not-audio guy, I have difficulties understanding some of the parameters. As the parameters are pretty technical, I guess there is no "simple" explanation. However, maybe there are possible improvements, hinting roughly at what effect e.g. the Windows size, the power floor and the frequency filter typically have.
I somewhat understand what the reduction amount means (I would roughly understand it as strength).

[AlisterH]

Hi, I don't have a good grasp of it; feel free to suggest any specific improvements, preferably with a pull request.