Noise Removal Tests

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Re: Noise Removal Tests

Permanent link to this post Posted by billw58 » Thu Apr 14, 2011 9:04 pm

Marco Diego wrote:Hi!
I discovered how to get rid of the artifact. The problem is caused because AudNR uses a too small FFT window. Setting mWindowSize to 4096 or 8192 (line 80 in NoiseRemoval.cpp) fixes the problem.
Most noise removal effects I've used have an option to set the fft window size. Shouldn't AudNR have this option too?

Woohoo! :D
Thanks, Marco.
Since this patch is so simple could you submit it and get is committed? Then I could try it out in the next nightly build.

What is the FFT window size currently set to?

Don't know about adding a control. I would welcome it, but less experienced users might be turned off, as Steve noted.

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Re: Noise Removal Tests

Permanent link to this post Posted by steve » Fri Apr 15, 2011 1:27 am

billw58 wrote:What is the FFT window size currently set to?

2048

Thinking back to the days when I used CoolEdit Pro, the current setting is toward the low end.
There's probably going to be some trade off - possibly on processing time / CPU load.
This calls for some testing. I'll see what I can do over the next few days.
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Re: Noise Removal Tests

Permanent link to this post Posted by steve » Fri Apr 15, 2011 8:33 pm

I've tested Noise Removal with FFT set to 8192

Compared with an FFT size of 2048, more noise is removed with less damage to the remaining sound.
The differences are most noticeable with "synthetic" tests (tones over low level noise), but also apply to real world test samples, though the improvement was generally quite subtle with the real world samples that I tested.

The low frequency artefacts mentioned previously are considerably reduced, and in conjunction with a slightly raised "Sensitivity" setting (around +4) are virtually eliminated.

High frequency damage can cause "denoised" audio to sound muffled. This unwanted effect is substantially reduced by using a larger FFT size.

In no tests were the results worse with a larger FFT size.

The down side is that processing time increased by around 20%.

The question is, do people want a relatively subtle improvement at the expense of slower processing?
I'm +1 for improved Noise Removal.
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Re: Noise Removal Tests

Permanent link to this post Posted by billw58 » Fri Apr 15, 2011 11:39 pm

steve wrote:In no tests were the results worse with a larger FFT size.
The down side is that processing time increased by around 20%.
The question is, do people want a relatively subtle improvement at the expense of slower processing?
I'm +1 for improved Noise Removal.


In my books the gold standard is Brian Davies' DeNoise program. I never use Audacity's Noise Removal (sic) effect. When Audacity's NR can produce results comparable to DeNoise then I'll be happy, and would be fine with increased processing time in exchange for an improved effect.

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Re: Noise Removal Tests

Permanent link to this post Posted by steve » Sat Apr 16, 2011 12:41 am

Real world sample here: viewtopic.php?f=28&t=55447#p137178
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Re: Noise Removal Tests

Permanent link to this post Posted by Marco Diego » Sat Apr 16, 2011 2:00 am

Great Steve! You've just shown that AudNR is now no longer too far from state of art noise reduction effects.

I have many changes queued for AudNR (you would be very happy to use my "own branch"), but they won't land in audacity anytime soon because of a "feature freeze" for 2.0. Some of my changes significantly reduce AudNR wooshiness and periodic artifacts (the intermittent sea-shell-like sound). So, I want to find a way so that I can post my changes and interested people can test it. I really need outside opinions and tests.

Do you have an idea on how we can achieve it?
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Re: Noise Removal Tests

Permanent link to this post Posted by billw58 » Sat Apr 16, 2011 2:30 am

steve wrote:The low frequency artefacts mentioned previously are considerably reduced, and in conjunction with a slightly raised "Sensitivity" setting (around +4) are virtually eliminated.

It would be nice if they could be eliminated without raising the sensitivity.

Did you try the noise in the presence of tone test that started this thread? I'd love to know if HF noise is now reduced in the presence of a mid-frequency tone.

What real-world samples have you used? My acid test is a decaying guitar note into noise. A decaying piano note would work as well.

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Re: Noise Removal Tests

Permanent link to this post Posted by steve » Sat Apr 16, 2011 2:29 pm

Marco Diego wrote:Great Steve! You've just shown that AudNR is now no longer too far from state of art noise reduction effects.

It's not as bad as it used to be.
Unfortunately at least one of the developers think that the current release version of NR is good :?
Having used many other Noise Reduction tools, there is IMO, still some way to go, but results so far are very encouraging.
I am personally very keen to see this feature improved as good Noise Reduction would be a very good "selling point" for Audacity, and it would save me the hassle of switching between applications when I have to clean up noisy source material.

Marco Diego wrote:I want to find a way so that I can post my changes and interested people can test it. I really need outside opinions and tests.
Do you have an idea on how we can achieve it?

As there are several different approaches involved I think it would be very helpful to have an overview page on the Audacity wiki. We could also have a set of test samples on there which would allow fair comparison between different NR methods.

Personally I find wiki formatting highly irritating and totally not user friendly, but in this case I think it would probably be the best format for holding an overview and a review of test results. If we include the posts in this topic, there have already been over 10 pages of posts on this subject, so I think an overview page is essential for keeping track of developments.

Since you (Marco) are most actively involved with developing this feature it would probably be best if you started off the wiki page, but if you're uncomfortable with posting to the wiki I could get it started off on your behalf.

For quicker and easier access to posting new patches, discussing ideas, and returning test results, I can make this a "sticky" topic on this forum board. This will hopefully encourage other Audacity users to contribute with ideas and test results.

billw58 wrote:Did you try the noise in the presence of tone test that started this thread?

No, not yet, but I'll try that.

billw58 wrote:My acid test is a decaying guitar note into noise.

Yes, that would be a good "revealing" test. That's exactly the kind of thing that I have in mind as part of a set of "standard" test samples.
Do you have a suitable recording with real world noise that you could donate?
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Re: Noise Removal Tests

Permanent link to this post Posted by Marco Diego » Sat Apr 16, 2011 5:38 pm

steve wrote:Since you (Marco) are most actively involved with developing this feature it would probably be best if you started off the wiki page, but if you're uncomfortable with posting to the wiki I could get it started off on your behalf.


Yes Steve, I would like better if you start the wiki page. However, there are some sections that I think are needed:

1 - An Introduction section saying that noise reduction is not an easy task and in this we collect some tests and experiments to check how the effect evolves with changes.

2 - An Experiments section that should contain a list of patches with descriptions of what they do, in which audacity version should be applied, who created, when was created and what improvement is to be expected.

3 - A Results section that would contain a list of noisy samples, their description, the best result achieved with a stock version of audacity (and the settings used) and the best result achieved with an experimental version of audacity (and the settings used).

4 - A conclusion section discussing the results and showing which experiments are more promising.

The beginning of the article should also contain the description of the above four points. That way, people interested in helping will be able to follow a "standard format".

If we do that, many people will be able to collaborate to improve AudNR, be it by making tests, commenting or posting audio samples.
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Re: Noise Removal Tests

Permanent link to this post Posted by billw58 » Sat Apr 16, 2011 7:44 pm

steve wrote:Do you have a suitable recording with real world noise that you could donate?

Not "real world", but decaying guitar harmonics with white noise added at -40 dB. The last second is just noise.

GuitarPlusNoise.flac
(713.05 KiB) Downloaded 106 times


I'll go through my vinyl collection. I think I have one that would be suitable. Stay tuned.

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