Noise gate augmentation

[shahules786]

Implemented spectral gating based on https://timsainburg.com/noise-reduction-python.html
Can you check this and let me know what you think? @iver56
I will implement the tests after the review if that's fine.

[iver56]

Thanks for the initiative! It would be nice if you could add it to the demo script as well, so we can listen to what it sounds like :)

[shahules786]

Thanks for the initiative! It would be nice if you could add it to the demo script as well, so we can listen to what it sounds like :)

Done.

[iver56]

I listened to an output from the demo script now, and I can hear a buzzy sound that was somehow added to my original sound. I did not expect this. Maybe something is wrong with the implementation? I can also see it in the spectrogram:

I expected something more like this:

(I created this "expected" example with Audacity's built-in noise reduction plugin)

Here are the 3 wavs that I compared in those two spectrogram gifs:
spectral_gating_sounds.zip