Verdict on the settings for new Noise Reduction?

[cyrano]

Seems to call for an "advanced parameters" button somewhere...

[waxcylinder]

You presumably have high quality audio with very little noise.

Well medium-plus quality - it is a webstream (and presumably carries some compression) - it's the (fairly noticeable) carrier hiss/noise that I'm removing.

And in the case of BBC FM R3 indeed high quality - but with some FM carrier to remove.

We may need to change the advice in the Manual to advise users to choke down the setting for music quality.

The advice may need to be subtly changed, yes. I think the current advice assumes music rather than speech, but clearly a lot of users are working with speech.

I'll see what I can do there - though I note that James has set the default at 3 and extended the range.

Peter.

[Gale Andrews]

I note that James has set the default at 3 and extended the range

I asked him to look at this topic and take some action or discuss it with us.

I hope 3 with a maximum of 12 is better than 6 with a maximum of 6, and that those with high quality music sources will have less trouble with 3 than with 6.


Gale

[steve]

I hope 3 with a maximum of 12 is better than 6 with a maximum of 6, and that those with high quality music sources will have less trouble with 3 than with 6.

For high quality music I find "3" to be marginally better than 6 (smoothing seems to have more of an "on/off" effect than in the old Noise Removal).
I think that "3 of 12" suggests that the slider should normally be set low, and (hopefully) may encourage experimentation.
The most problematic noise that I'm finding is low level but uneven noise - in such cases I want the smoothing factor as low as possible (to minimise damage), but that runs the risk of slightly higher noise "breaking through" as tinkles.

[Gale Andrews]

smoothing seems to have more of an "on/off" effect than in the old Noise Removal

Meaning that there seems less discrimination between lower and higher smoothing values? Perhaps, though I certainly hear the difference between 3 and 12, which higher value I now don't have to type in.

I agree there is not much difference between 3 and 6.

Is "less discrimination" because of the different units (bands and not Hz)?

The most problematic noise that I'm finding is low level but uneven noise - in such cases I want the smoothing factor as low as possible (to minimise damage), but that runs the risk of slightly higher noise "breaking through" as tinkles.

That risk is my issue exactly.

But it seems a weakness in the algorithm if it cannot respond to variations in the level of the same noise. And if the noise type changes, it's defeated.


Gale

[Paul L]

Default smoothing will be 6 in future versions.

I am pleased we finally increased default smoothing, but don't you think it looks odd to have a default at the extreme of a slider scale?

Gale

My thoughts too.
The extreme should in any case be higher - 10 or 12.
If I'm correct, 6 is approx. 150 Hz and we used up to 500 Hz in the old effect. This might not be necessary anymore with the partially new algorithm but who knows.
What about a track with 16 kHz sample rate?

Robert

Remember that frequency smoothing counts bands now. The equivalence of 6 to the old 150 Hz assumes a 44100 sample rate.

So what is the equivalence of 6 at for example 96000 Hz, or 8000 Hz or 16000 Hz (which a voice track might be)?

It seems you are still discouraging frequency smoothing above 6 by setting 6 as the maximum. Are you so discouraging?

https://soundcloud.com/blizzkrut/sets/a ... nd-problem which is voice with heavy noise (or a normalized version with DC offset removed) needs more than smoothing of 6 in my opinion to reduce artifacts on the voice in the noise-reduced result.

What settings would you use on that? The Forum topic those samples comes from is http://forum.audacityteam.org/viewtopic ... 46&t=87385.


Gale

If I don't err, the smoothing over 7 bands (since factor 0 = 1 band) for different sample rates are as follows - all in Hertz, except last column:

Code: Select all

Sample Rate	Bandwidth	Smoothing factor
8000	27.34375	37.5875
16000	54.6875	18.29375
22050	75.36621094	13
32000	109.375	8.646875
44100	150.7324219	6
48000	164.0625	5.43125
88200	301.4648438	2.5
96000	328.125	2.215625

The last number shows the factor needed to get the same 150 Hz band width as with 44100/6.

Of course, the window length in seconds changes as well and thus the results are presumably not comparable - I haven't made all the tests needed.

Robert

How did you calculate those numbers?

A "band" means a "bin" with a 2048 sample window. It is the higher sample rates that have narrower bins.

[Paul L]

Ah well, that might be remedied by allowing the attack and release sliders to be visible again, (release more so than attack,) which is another debate.

It's a debate that we had about 12 months ago.
A problem adding more controls is the high degree of interdependency between controls.

don't you think it looks odd to have a default at the extreme of a slider scale?

Yes. We have jumped from one extreme of the trade-off to the other.

Perhaps the debate needs to be reopened. It was decided summarily by somebody else when I did not have commit privileges, but I was for including those sliders, so that decaying percussive notes could sound better. You may wish to uncomment
// #define ATTACK_AND_RELEASE
and see if you can improve your musical example with a longer release setting.

[Paul L]

It seems you are still discouraging frequency smoothing above 6 by setting 6 as the maximum. Are you so discouraging?

The higher the "smoothing" factor, the more damage is done by the effect.
It may not be so noticeable with speech recordings. but with high quality music recordings the damage is very evident with the new default settings if you listen to the decay of notes.

As a simple demonstration:

1) Generate a few seconds of Pink Noise and Normalize to -46 dB (about -60 dB RMS). This is a reasonable good approximation of low level noise that one might want to remove from a good quality original recording.

2) Import a really good quality music recording that has very low noise - piano music would be a good choice for demonstration purposes.

3) Create a noise sample from the Pink Noise

4a) Apply to the piano music with "Residue" selected. Note how much of the music is present in the residue.
4b) Apply to a mix of the noise and the music - notice how the notes decay much faster than the original.

Yes, I know. I dislike that, and I sometimes miss the ability to control the release.

But the whole thing is a trade off. With higher noise levels, or quieter music, the loss of attack can be subjectively less bad than artifacting.

Are you assuming attack and release must be coupled? That is not so, I made them separate controls.

Ah well, that might be remedied by allowing the attack and release sliders to be visible again, (release more so than attack,) which is another debate.
It's a debate that we had about 12 months ago.
A problem adding more controls is the high degree of interdependency between controls.

It is a problem, but more controls could be hidden behind an "Advanced" checkbox, or perhaps separated into another box.

JC opposed the idea of "Advanced" settings and I believe blocked the attack and release sliders because no one had written good enough documentation.

Also do we have to have the interdependency? Could some filter to mask artifacting be applied "over the top" of the effect, like some kind of post-processing?


Gale

I do not understand. Frequency smoothing is indeed already a post-processing which is the last step in the calculations.

[Paul L]

smoothing seems to have more of an "on/off" effect than in the old Noise Removal

Meaning that there seems less discrimination between lower and higher smoothing values? Perhaps, though I certainly hear the difference between 3 and 12, which higher value I now don't have to type in.

I agree there is not much difference between 3 and 6.

Is "less discrimination" because of the different units (bands and not Hz)?

The old effect's frequency smoothing really did vary discretely with bands too, but this was not documented.

I made a change from an arithmetic to a geometric averaging of gain factors when figuring the smoothing -- which made more sense, multipliers make more sense when averaged that way, and I think it restored Dominic's original intent which got damaged by other hands in intervening years.

But I think that is a subtlety that would not account for the differences you notice.

The most problematic noise that I'm finding is low level but uneven noise - in such cases I want the smoothing factor as low as possible (to minimise damage), but that runs the risk of slightly higher noise "breaking through" as tinkles.

That risk is my issue exactly.

But it seems a weakness in the algorithm if it cannot respond to variations in the level of the same noise. And if the noise type changes, it's defeated.


Gale

The old effect would not have been better on that score. Both versions take just one noise sample to train on, and have no notion of adaptiveness to a changing background.

[Gale Andrews]

The most problematic noise that I'm finding is low level but uneven noise - in such cases I want the smoothing factor as low as possible (to minimise damage), but that runs the risk of slightly higher noise "breaking through" as tinkles.

That risk is my issue exactly.

But it seems a weakness in the algorithm if it cannot respond to variations in the level of the same noise. And if the noise type changes, it's defeated.


Gale

The old effect would not have been better on that score. Both versions take just one noise sample to train on, and have no notion of adaptiveness to a changing background.

Must we retain the existing algorithm in perpetuity?

Another "Advanced" setting could be a different algorithm.


Gale