Noise Removal Tests

Tested on Mac. No response to HOME and END keys, nor to mouse wheel. Arrow keys work fine. Changed OS to Windows/Linux.

– Bill

I wouldn’t do that (default Sensitivity to other than 0). My experience seems different from Gale’s: high sensitivity settings produce more artefacts and affect the desired audio.

– Bill

In searching for “audio noise reduction algorithm” I found this site:

Any comments? Anything here we could use for our wiki?

– Bill

Not so IIRC Gale - I seem to recall many posts on the forum on click/pop processing in Audacity and its limitations/weaknesses - many of which we push in the direction of Brian’s ClickRepair - well Bill and I do anyway :sunglasses:

And I seem to recall stevethefiddle doing some work on trying to produce an improved click remover a while back.


Using Gnome Wave Cleaner I was able to reproduce a similar kind of “beat” effect that we see in Audacity NR.

The settings to produce this sample were using a Blackman windowing function and “Power Spectral Subtraction” as the Noise suppression method.

When switching back to the recommended “Hanning-Overlap-Add” windowing function and “Lorber and Hoeldrich” as the Noise suppression method, the result was very much better.

Thanks, Bill. Leland’s accessibility patch for Mac may well help with that, if he is able to get himself in a position to commit it sometime.

No, I found the same increase in artifacts with higher sensitivities when testing quiet piano and string samples, and less noise removal with single piano tones than with spread piano chords. The artifacts themselves though were to me much less pronounced/much more in the bounds of tolerance than those occurring with tones.

With the effect as it is now, there may not be much noise removal with the Sensitivity slider at 0 if there is wide band noise and narrow band audio. If that was a common scenario (I assume it isn’t) then we’d have to have a default Sensitivity setting that removed a reasonable amount of noise, in my book. If not, it would be like having default Noise Reduction at zero.

Don’t recall Steve’s work on that - it’s only since this April when I’ve been paying more than cursory attention to the Forum. From comments I see elsewhere there are still more gripes about NR than click removal, in so far as people accept Effect > Repair is a good click remover… but it’s not feasible for whole tracks. OTOH with some noise, you just can’t remove it cleanly in Audacity (1.2 or 1.3), but (probably) can elsewhere.

Did anyone try Leland’s or Danni’s work combining Find Clipping with Repair? I had concerns how it could remove clipping on all of a track given Repair needs audio outside the selection, but I never tried either.

Perhaps we need P4 enhancement summary issues to improve NR and Click Repair. If there is no further technical input, perhaps we’ll just have to generalise the Wiki NR description a bit. I think the Manual is OK because it doesn’t really discuss anything where what happens is unclear, except for linking to the Wiki.


That was a long time ago - it was a Nyquist plug-in aimed at removing BIG clicks. It was not intended as a replacement or even an augmentation to the current Click Removal, but rather an extra tool (experimental) for dealing with the specific case of very large clicks that are missed by Click Removal and too numerous for using Repair. It did work, though not surprisingly it created a significant degradation to non-click sound… I’d just about forgotten about that plug-in, but it’s here:

Sounds like a good idea - perhaps broadening the scope to “Audio Restoration” (so including Clip Fix and Repair).


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?

Thanks for the tip Marco, I’ll try increasing the FFT size on my next build.
Whether or not to include a control in the user interface is a balance between how much benefit the control gives, against increasing the apparent complexity of the effect.
Some users complain that Noise Removal is already too complex with too many controls.

Steve, can you make a bunch of tests and come up with an optimal value for the FFT window size?

If the problem is AudNR becoming too complex, we can set a “global value” for FFT window size. A value that would be used by every audacity effect that uses FFT. The FFT window size would then be set from a single point in the UI, maybe the preferences window. What do you think about it?

Woohoo! :smiley:
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.

– Bill


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.

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.

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.

– Bill

Real world sample here:

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?

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.

– Bill

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 :confused:
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.

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.

No, not yet, but I’ll try that.

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?

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.

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

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

– Bill