Question for NR gurus...

[takearushfan]

Hi all,
I've noticed that sometimes noise reduction works just as I'd like it to. However, there are times when it makes the altered track sound as if it's underwater. What causes this and how can I avoid it while still eliminating a good deal of noise?
Thanks,
Justin

[redwudz]

Any audio filtering is a removal process. You take too much out and you get bad audio. Just use it sparingly and sometimes that's as good as it gets.

If your noise is in the same frequencies as your main audio, as in voices, you don't want to overfilter. If the noise is in the upper or lower frequencies, you can get away with a bit more. Static or white noise is just about all frequencies, so very difficult to remove. Start with your high and low filters and stay away from the midrange as much as possible, especially if voices are your concern.

Pattern noise, like 60hz hum or any very repetitious noise can sometimes be removed without much damage, depending again on the frequency.

It's pretty easy to make 'telephone' audio if you clip out the highs and lows too much.

[takearushfan]

Actually it is vocal stuff. A female's voice. To make it even harder to clean up, her "s"'s create their own kind of hiss :/

[Soopafresh]

You can find several De-esser plugins which should reduce the problems with "S" sounds.

http://www.digitalfishphones.com/main.php?item=2&subItem=5 Spitfish

You can load it into Wavosaur or your favorite VST compatible audio editor.

http://www.wavosaur.com/

[takearushfan]

Thanks, btw. Sorry for the delayed reply.

[3dsnar]

1. You need a good noise reduction software (there are only few worth recommendation). E.g. standard deNoiser VST plugin in Wavelab 4.0 or newer is an excellent tool.
2. The noise has to be stationary (constant amplitude and frequency characteristics over time) to achieve good results
3. When denoising, you need to select a noise fragment for spectral subtraction operations (spectral representation of the nois). You have to make sure that the fragment does not contain any of the useful signal. The longer fragment, the better spectrum estimation.
4. Leave a bit of noise in the recording, because spectral subtraction affects noisy transients of the useful sound. DeNoising by 6 dBs produces good results. No more than 18 dB (normally) is recommended
5. Sounds with too much noise cannot be restored very well, because useful sounds phase gets randomized and during the denosing process unpleasent artifacts are generated.
6. Deessing is a different operation than noise reduction.
7. II hope I could help

Cheers,
3d

[takearushfan]

To be honest, though I appreciate the replies, I used the wrong term. I'm not so focused on NR, rather I'm trying to reduce hiss. Just FYI, this is a film soundtrack from '79 that sounds like it was taken from someone's bedroom closet. I can't belive how bad it sounds, but I digress
- Justin

[redwudz]

If someone already messed it up, that's a little harder to fix. I'm familiar with the 'muffled' effect from too much NR. They may have had a low audio level and boosted it, along with all the noise. About all I can suggest is to play with the filter adjustments a little and see if you can get an improvement.

They may have also destroyed the dynamic range by overfiltering.

I use Audacity most times. Maybe 'Compressor, Equalization, FFT filter'. One or a combination. Just use a short representative clip and you may be able to make some improvements. I've been able to improve on the 'muffling' a few times by boosting and cutting the frequencies selectively.

But I'm definitely a novice with audio.

[Soopafresh]

Hiss is tough to remove. Post a 10-20sec clip of the problem.

[lordsmurf]

There are several ways to do audio NR. I prefer SoundForge, as it tends to be fairly easy to customize the noise removal filters, and the filtering can range from mild to harsh.

Something like Goldwave I use too, but it's a harsh filter kit.

There are other methods out there too, some of them hardware-based. I've dabbled in these for special needs, but SoundForge takes care of 90% of audio issues I run across (hissing, tonal loss, etc).

[takearushfan]

Well, I'm using Audition and there are presets for both NR and hiss reduction, but they're either too harsh or too soft. I can't seem to find a middle ground.

[Soopafresh]

Post a clip