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Removing noise from 8-bit audio

I'd like to try to remove the high quantization noise from some 8-bit audio I've acquired, even if it means converting it to 16-bit or something.  Normal noise-filter algorithms won't work because the noise only exists when the audio signal is active, meaning there is no section of the music with only the noise & so a noise profile cannot be made.

Does anyone have any suggestions?  Here's a sample of one of the files I'm looking to de-noise:
http://ourworld.cs.com/YWingCDG/theme00cut.flac

Removing noise from 8-bit audio

Reply #1
I'd like to try to remove the high quantization noise from some 8-bit audio I've acquired, even if it means converting it to 16-bit or something.  Normal noise-filter algorithms won't work because the noise only exists when the audio signal is active, meaning there is no section of the music with only the noise & so a noise profile cannot be made.

Does anyone have any suggestions?  Here's a sample of one of the files I'm looking to de-noise:
http://ourworld.cs.com/YWingCDG/theme00cut.flac

Apart from low-pass filtering I'm not sure there is much that you can do.

Removing noise from 8-bit audio

Reply #2
Normal spectral noise subtraction algorithms can still work surprisingly well when creating noise profiles derived from non-silent sections of source material, especially if the profile section is long enough and doesn't contain tones that sustain for too great a proportion of the profile section. The noise itself is essentially "statistically stationary" for the duration of the noise profile selection, so providing the desired signal is not statistically stationary enough to be important in the average, you can still get fairly decent results if you don't apply the effect too strongly.

The alternative, if it's purely down to a conversion, would be to create a known signal at 16-bit or more and render it to 8-bit in a way comparable to the original to generate the noisy signal then convert back to 16-bit and subtract from it the original known signal to generate a profile of pure 8-bit truncation/dither noise. If this happens to match the noise in the original sufficiently well, it could allow decent noise reduction. A circumstance where this might be possible is where you still own your 8-bit card but can sample its output on a newer 16-bit or better card. If you play a known 16-bit source through the 8-bit card, you can play a known 16-bit source via the 8-bit card and sample it, then subtract the original from the 8-bit (if you can time-align adequately) to obtain a pretty pure noise profile.
Dynamic – the artist formerly known as DickD

Removing noise from 8-bit audio

Reply #3
I'd like to try to remove the high quantization noise from some 8-bit audio I've acquired, even if it means converting it to 16-bit or something.  Normal noise-filter algorithms won't work because the noise only exists when the audio signal is active, meaning there is no section of the music with only the noise & so a noise profile cannot be made.


You can generate 16-bit wav with silence and convert it to 8-bit using rectangular or triangular dither. This white noise can match your needs very well.

Removing noise from 8-bit audio

Reply #4
My knowledge regarding the inner workings of noise-filtering algorithms is absolutely zero, but I just threw your sample at Audacity and ran the "Noise Removal..." option feeding it the first 1.5 seconds as the reference and using the lowest setting and it certainly removes the vast majority of the noise. Goodness knows what else it's removing as I've never heard the original source material, but it's kind of listenable for a 22kHz 8-bit sample.

Cheers, Slipstreem. 

Removing noise from 8-bit audio

Reply #5
Thanks for the help!  I did just what you said, Dynamic, about subtracting a 16bit->8bit file from the original 16bit to get my noise profile, and it works pretty good! 

 

Removing noise from 8-bit audio

Reply #6
Goodness knows what else it's removing as I've never heard the original source material, but it's kind of listenable for a 22kHz 8-bit sample. :D


Some of the noise reduction apps let you keep the noise you would have removed instead of keeping the de-noised version, so it gives you some idea of what has been removed and whether it sounds too much like stuff you'd like to keep (or too loud in comparison to the original). I think the old CoolEdit96 did, so I expect CE2000 or Adobe Audition would do the same.

I'd suggest to Moguta that you try more than one method of generating the noise profile to see which seems to work best. Also some NR apps work better than others.
Dynamic – the artist formerly known as DickD

 
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