Noise reduction in sections of a track

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mwhelm
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Noise reduction in sections of a track

Post by mwhelm » Sun May 09, 2021 1:03 am

I have an on-going audio digitization project. The material has noise reduction issues. I'm looking for ways to simplify the handwork.

This material is old, but valuable. Most of the recordings have a lot of hum and noise - nowhere near enough to make it unlistenable, but annoying. It's easy to make listening much more comfortable with very light noise reduction.
Lectures & musical tracks are not much of a problem. Often noise reduction can be skipped, it's not obvious enough to most people to be a problem. I suppose it might be subliminally an energy drain on the listener, but don't know.

Guided meditations make up a lot of the content, and they are a problem. The normal pace of these is often
Talk,talk,talk, <silence for 30-300s>, talk,talk,talk, <silence for 30-300s> &c

During those silent periods, the fluorescent induced hum, the crackling, and buzzing just jump out because of how the material is used - this noise really needs to go away. I've found that I can either de-amply the sound in the gaps by -50db or do noise reduction at a very high level, effectively silencing the non-talking period; either work well.

The problem is the hand labor with these guided talks. Is there a way I could select more than one segment in a track & apply this reduction to all of them at once? A way to script this? A way to apply high level NR to all sections of the track that are below some db limit? Some other idea? Any ideas appreciated.

kozikowski
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Re: Noise reduction in sections of a track

Post by kozikowski » Sun May 09, 2021 3:24 am

Which Audacity are you using? You may be working too hard. Analyze the noise. If it has a strong power line component, you might be able to apply a hum remover followed by medium noise reduction to the whole show.

You might be a candidate for a Noise Gate. 'Watch the sound level and reduce the sound even further if the raw show drops past a certain loudness. Many people think you need to crush the quiet parts to zero, but these tools can be used more gracefully at smaller values. Hum Remover, gentle noise reduction and a small value of noise gate may do it for you—without programming or scripting.

Macros can't make decisions. They can't go looking for errors or gaps in the show. There is no IF/THEN. IF the voice drops out, THEN do processing. Sorry. It can't do that.
Koz

kozikowski
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Re: Noise reduction in sections of a track

Post by kozikowski » Sun May 09, 2021 3:28 am

Post some of it. If it's mono, one blue wave, you can post up to 20 seconds of perfect quality WAV. If it's stereo, you're limited to 10 seconds of WAV. Stay away from MP3. MP3 creates sound distortions and you can't stop it.

Include two or three seconds of noisy gap and the rest dialog or show.

Scroll down from a forum window > Attachments > Add Files.

Koz

mwhelm
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Re: Noise reduction in sections of a track

Post by mwhelm » Tue May 11, 2021 7:52 pm

Audacity 3.02 on Windows 10
I have encountered the "uncanny valley" feeling of having all the sound gone, but it's better than the buzz.
Even the ability to select multiple segments & then apply the same NR to them would be a big work flow improvement.
As far as coding goes, I was wondering if something like
if ( db < some value over some time) ) apply deep NR

I attach a snippet as requested from one I worked on today. It's far from the noisiest but it's over the edge of where I would suppress the hum, & the hum is typical.

I've gotten hypersensitive to the hum in the lectures &al but I don't think most people really hear it. On the other hand the gaps / quiet periods, it's really unwelcome.

Thanks, ==mwh
Attachments
AUDexamp.wav
Small snippet
(1.7 MiB) Downloaded 6 times

jademan
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Re: Noise reduction in sections of a track

Post by jademan » Wed May 12, 2021 6:37 pm

I applied Noise Reduction with the defaults 12 6 3 to your sample after getting the noise profile, and could then hear no audible background noise.

mwhelm
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Re: Noise reduction in sections of a track

Post by mwhelm » Wed May 12, 2021 7:05 pm

I applied Noise Reduction with the defaults 12 6 3
Thanks, but I know how to do that.

That's not the solution to the problem I pose.

kozikowski
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Re: Noise reduction in sections of a track

Post by kozikowski » Wed May 12, 2021 8:04 pm

I think you win the prize. The clip has tape hiss (no surprise there) and European power buzz (50Hz and harmonics) and also "Stuff." It's the Stuff that's going to be a problem. I can't identify it enough to know the best way to suppress it other than, as as Jademan, above, the blunt force tool of Noise Reduction.

So I rolled up my sleeve and generated a recipe of tools. No one tool is taken to extremes, so the voice survives unharmed. You can still hear some hum between words if you search for it.

This has the advantage that you run the tools one time at the beginning no matter how long the show is.

AUDexamp-patched.wav
(1.7 MiB) Downloaded 6 times

If that works for you, I'll post the list.

Koz

kozikowski
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Re: Noise reduction in sections of a track

Post by kozikowski » Wed May 12, 2021 8:13 pm

The first tool is a little odd. It reduces rumble, thunder, and thumpy noises. You can't hear most of it by way of a casual listen, but very low-pitch noise can affect the other tools.

The noise in the gaps is about -80dB if you're counting. Again, this is several tools all working on each other's efforts. No single magic wand tool.

The voice volume has been boosted, too, so watch the volume when you play the sample.

Koz

mwhelm
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Re: Noise reduction in sections of a track

Post by mwhelm » Thu May 13, 2021 11:58 pm

That sounds pretty good to me.
Boosting the voice is (usually) one of the things I have to do with this material.

This sounds better than what I have been managing. I'd like to apply this recipe on some longer silent tracks & some of the bad quality tapes & see what more can be done.

Please post the list! Thanks, ==mwh

kozikowski
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Re: Noise reduction in sections of a track

Post by kozikowski » Fri May 14, 2021 12:43 am

If I did it right, it shouldn't make any difference the volume you start with. It's self-correcting. If it's too far off, you'll just get perfect volume trash.


OK. I rolled up the other sleeve:

Select the whole show.

Effect > Filter Curve : Low Rolloff for Speech > OK.

Low Rolloff.png
Low Rolloff.png (89.77 KiB) Viewed 128 times

Effect > Amplify > Goal (second window) -1dB > OK

Amplify.png
Amplify.png (29.96 KiB) Viewed 128 times

Effect > Hum Remover: Europe, 13,1,10 > OK.

Hum.png
Hum.png (41.65 KiB) Viewed 128 times

Select some noise only. Effect > Noise Reduction > Profile.
Select the whole show > Effect > Noise Reduction > 12, 6, 6 < OK

NR.png
NR.png (84.81 KiB) Viewed 128 times

Effect > Noise Gate > Level -12, Gate -40, Attack 250 > OK.

Gate.png
Gate.png (59.04 KiB) Viewed 128 times

Let's see if you get the same results I did.

I need to lie down.

Koz

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