Strange oozing sound after using noise reduction

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Strange oozing sound after using noise reduction

Permanent link to this post Posted by vinckles » Mon Jul 17, 2017 1:20 pm

Windows 7 32 bit pc 1 gb of Ram Memory. (My pc used to be 4gb Ram Memory but not anymore.)

Well, after watching dozens of youtubes and reading many articles about separating sound from video; then converting the audio into a WAV file; then pushing the WAV through Audacity and using Noise Reduction to get rid of hiss, ( a process I have always dreamed of doing), I finally took the plunge to do just that!

I have two television shows, probably recorded on tired old vhs which have very hissy sound tracks. I worked the above mentioned procedure to remove the hiss and at first glance I was elated with the results. Then missery: Although the hiss was completely gone, I found that 4/5ths into the playback, all speech was effected by an awful "oozing sound"; rather like they were speaking through a long tube. This problem applies to both my videos.

I have since read an article online claiming that Noise Reduction in Audacity should be avoided at all costs and that Equalisation should be used to get rid of hiss instead! So after all those youtubes etc, re Noise Reduction cleaning it seems we have all been led down the garden path(?)

Audacity Noise Removal seems to be the cause of the nasty "oozing sound". What is the truth here? Is there something I can do to make the Noise Reduction method a good success or should some other technique, such as EQ cleaning be adopted?

I am brand new to Audacity and am still trying to 'learn the ropes'. Hoping someone can end my misery and disappointment. Regards
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Re: Strange oozing sound after using noise reduction

Permanent link to this post Posted by steve » Mon Jul 17, 2017 2:05 pm

Noise reduction is a balancing act (and this is not unique to Audacity, it applies to all applications that have noise reduction).
The Noise reduction effect tries to identify noise, based on the "noise sample" that you provide it with, and then to reduce the level of that noise throughout the processed audio without doing too much damage.

The effect in Audacity works extremely well in cases where there is constant, low level noise, and a strong clear signal, but the effect is not magic. If the noise level is high, or the noise changes, or the signal level is low, then it is more difficult for the effect to work out what is noise and what is sound that you want to retain. Attempting to reduce the noise too much will incur damage to the sound that you want to keep. Setting the effect too gentle will leave more noise in the recording than necessary. So you need to strike a balance between how much noise is acceptable, and how much damage to the remaining sound is acceptable.

The default settings of 12, 6, 3 will generally give a good amount of noise reduction without causing too much damage.
For high quality audio work where the noise level starts off very low, more gentle settings of 6, 6, 3 are usually better.

Using Equalization to reduce hiss is usually less effective than noise reduction, though the "damage" is of a different kind. Reducing the treble will reduce hiss, but at the cost of making the retained sound muffled.

There's no substitute for starting with a good clean recording. When we can't do that due to circumstances beyond our control, we are on a rescue mission and have to try to salvage as much as we can, but it will never be pristine.
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Re: Strange oozing sound after using noise reduction

Permanent link to this post Posted by DVDdoug » Mon Jul 17, 2017 2:14 pm

Noise reduction works best when you have a tiny, constant background noise. If the noise is bad, sometimes, "the cure is worse than the disease". :(

...Pros still record in soundproof studios with good equipment and good mic placement.

You may find a better compromise by playing with the settings, or low-pass filtering/EQ may be a better compromise, or it may be best left as-is. That's for you to decide.

If you low-pass filter, you can try using the Harmonic Enhancer Effect to "restore" the highs.
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Re: Strange oozing sound after using noise reduction

Permanent link to this post Posted by kozikowski » Mon Jul 17, 2017 3:07 pm

Just a note, the earlier Noise Removal did that wine glass sound as a normal course of events and was almost completely useless in the face of hiss. I'm pretty certain that was the source of the posts about not using the noise tools at all. It's true. Although others liked it, I never got Noise Removal to do anything useful.

Audacity 2.1.3 Noise Reduction is much more gentle about it's job and light applications are recommended if you have a particularly noisy microphone, for example, in AudioBook reading. The AudioBook companies hate processing and they can't hear it being used.

So we can start there.

http://www.audacityteam.org/download/windows/

If you have extended-play VHS tapes before VHS HiFi, your tapes have a terrific amount of tape noise hiss and the best you can do is reduce it a little. Nobody wrote you can make it go away. That's not in the cards. We intentionally changed the name of the tool because too many people were expecting Noise Removal to remove all the noise. To zero. Neither tool will do that.

One problem you may have is executing the noise profile step. You have to drag-select a portion of the show that is noise-only to give the tool some idea what you want it to do. A very common problem with very noisy work is an inability to find a segment without show in it, and if you include any voice or music by accident, Noise Reduction will try to remove the voice or music, too.

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Re: Strange oozing sound after using noise reduction

Permanent link to this post Posted by vinckles » Wed Jul 19, 2017 7:42 am

Thank you to all who replied.

The terrible "oozing sound" is not noticeable throughout most of the 50 minute audio recording. It only appears about 5 mins from the end.
The second recording lasts 25 mins and again is clean up to 5 mins from the end.
That must be significant, is it not???

I only downloaded Audacity on 8 july 2017, so I suspect it is the very latest version.

I have been relentlessly searching for help with this problem: One forum thread simply said change to old version 1.3.7 since it had better noise removal characteristics.
Another thread said turn the noise level down to half way. I have not touched any of the settings. I am brand new to Audacity. I figured everything would work good on the defaults.

If others are not NOT experiencing this "oozing", "bubbling" sound on the very latest version towards the final 1/5th of their recording, then clearly the problem lies with my equipment(?) Does anyone know what this might be, please?
a
(Just to be thorough: I am using windows 7 32 bit 1gb Ram Memory. I converted the video to WAV using Eusing video converter; I then pushed the WAV through Audacity and found a 20 second segment of silence / hiss; worked the usual routine to Reduce noise, but upon inspection the "oozing" sound was all too clear at the tail end of the recording. It's majority sounded good.
Another recording I tried produced the very same result. Why does it only attack the endings for a minute or so, whilst the rest of the show is great?)
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Re: Strange oozing sound after using noise reduction

Permanent link to this post Posted by steve » Wed Jul 19, 2017 10:23 am

vinckles wrote:I only downloaded Audacity on 8 july 2017, so I suspect it is the very latest version.

That depends where you downloaded from.
The Audacity website always has the current version: http://www.audacityteam.org/download/
Other websites may have old versions, or even hijacked versions containing viruses, which is why we ask for the exact version number (which you can find at the top of "Help > About Audacity") and recommend to always use the download links on the Audacity website. The links on the website currently download from our trusted CDN (content distribution) partner FossHub.

vinckles wrote:The terrible "oozing sound" is not noticeable throughout most of the 50 minute audio recording. It only appears about 5 mins from the end.
The second recording lasts 25 mins and again is clean up to 5 mins from the end.
That must be significant, is it not???

I think we need to hear this in order to make progress. Please post some short samples in WAV format to illustrate.
See here for how to upload audio samples: https://forum.audacityteam.org/viewtopi ... 49&t=72887
Each sample needs to be only a few seconds long - just enough to illustrate what you mean.
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