Re: [Audacity-devel] [PATCH] Improvement for Noise Removal effect V7

[Steve t. F. <ste...@gm...>]

Firstly, a big thank you to Marco for all his work on this.

Having now done quite a lot of testing (Audacity 1.3.13 / Linux), I am much
happier with the effectiveness of the Noise Removal effect than previously.
The "Sensitivity" slider makes a substantial improvement for certain types
of material where previously noise was evident "behind" the non-noise
signal.

The Attack/Decay slider is now functional and really helps to minimise
"wooshing" / "fluttering" effects.

I have also found the "isolate" switch to be a useful feature.

However, there's a couple of little bugs remaining.
The "Sensitivity" and the "Attack/Decay" sliders do not respond correctly to
the cursor keys (or mouse wheel).

Regarding the suggestion of "inverted noise isolation", I think this is an
interesting idea, but in terms of assisting "mixing" the amount of noise
reduction I have not found it to be very effective. Invariably I have been
able to achieve better quality noise reduction through tweaking the
currently available slider. Although I'm not sure what causes the
difference, reducing the "Noise Reduction (dB)" will invariably produce
better results than setting it higher and mixing some of the noise track
back in.

I have found certain situations where the "invert and mix" method does come
in useful - in one audio sample that I tested, due to the type of musical
material, best results were obtained using different settings at the
beginning and end of the piece to the settings in the middle of the piece.
By using multiple copies and the "invert and mix" technique I was able to
"slide" from one setting to another. However, I think this would definitely
be classed as an "advanced" (or obsessive :=) technique, so I think that
while it may be worth writing up in the wiki, it should be left out from the
interface.

Regarding the Sensitivity scale:
All the material that I have tested has indicated best results in the range
of 0 to +20 dB.
As the Sensitivity control is increased, the "damage" done to the audio is
always increased (more of the non-noise signal is removed). This will
sometimes produce subjectively better results (which was the point of this
whole thing), but my tests indicate that +20 dB is a sensible limit. None of
my tests indicated that further improvement could be made by pushing the
slider beyond +20  dB.

Regarding negative settings. The only use that I found for negative settings
was when trying to deliberately cause "damage" (artefacts as an effect). In
no cases did negative settings produce better noise removal than zero or
positive settings. Is it worth keeping the negative settings to allow the
user to deliberately cause artefacts, or would it be better to set the range
to positive values only? As this is effect is called "Noise Removal", and
the stated purpose is for removing noise, my vote would be to keep only
those settings that aid noise removal. I think the Sensitivity scale should
be from 0 to +20.

Some of the noise samples that I used are available here:
http://audacity.easyspacepro.com/examples/noise-samples/

Steve D