Could someone please elaborate for me exactly what Audacity Noise Reduction does. Does it. for example, take out all sound of the same level as selected (thus potentially removing some wanted signal ?) Or does it in some way try to match the pattern of the selected signal ?
I think you should be able to find everything via this page: http://manual.audacityteam.org/man/noise_reduction.html
I did read that previously, but it didn’t do it for me. However, looking at it again, particularly things like ‘noise floor’ and ‘residue’ does help.
The “Advanced Tips” at the bottom of that page may be of interest.
(thus potentially removing some wanted signal ?)
Yes, there can be artifacts and sometimes, “The cure is worse than the disease.”
Noise reduction works best when you have a constant low-level background noise… It works best when you don’t really need it.
There’s a reason pros still record in soundproof studios with good low-noise equipment.
I had good results recently with a very noisy digitized vinyl record. It’s an acoustic guitar recording and I was pleasantly surprised with the lack of audible noise-reduction artifacts. Maybe acoustic guitar is more immune than other sounds, or maybe Noise Reduction is improved since I last used it. …But, it only removed the “background” noise and I’m still working on the “snap”, “crackle”, and “pop” with a special-purpose application called Wave Repair (and that’s after running Wave Corrector).
Vinyl is a special case. The character of that sound doesn’t easily fall into general noise or distortion categories. However, it’s so popular, special purpose tools have been designed.
I don’t know that the instructions stress enough how important the Profile step is. That’s where Noise Reduction “sniffs” the work you hate. That’s how it knows what to reduce. There is no good provision to use Noise Reduction if you can’t get a good, clean Profile. My nearly-true joke is not to get a little of your voice in the Profile by accident. Noise Reduction will try to remove your voice.
A very common failing of Noise Reduction is overuse. It’s easy to miss the odd sound or voice distortion produced by excessive processing because you’re only listening to the background noise. The background is velvety quiet, but the show is beginning to sound like a cellphone.
The early Audacity tool was called Noise Removal. It was changed because too many people wanted it to remove noise…completely.
Neither tool will do that.