Sound quality reduced while using "Noise Removal"

OS: Win 7 Ultimate
Ver: 2.0.5

Ive tried to eliminate background noise with noise removal. Ive highlighted a part dedicated to get the background noise, and then pressed Get Profile. Ive then played it and the background noise was eliminated, but in the process the sound quality was reduced and speech was incomprehensible. Is this an expected side effect or there is a away to eliminate background noise (or reduce it at least) and retain speech quality?

Noise “Removal” is probably not a good name. Better would be Noise “Reduction”.
Reducing noise is always a trade-off between the amount of (bad) noise removed and the quality of the (good) audio that is retained. Attempting to “eradicate” the noise will invariably have a bad effect on the quality of the remaining sound.

Ironically, the Noise Removal effect works best when the background noise level is very low. The higher, and the less constant the background noise is, then the harder it is to effectively reduce without causing bubbly metallic artefacts in the remaining sound.

The “art” in using Noise Removal effectively is:

  1. Start with as good an original as possible. The less background noise the better.
  2. Select a good “Noise Profile”. This should be only the constant background noise and no other sounds. (You can’t expect the effect to remove the sound of a TV in the background, because to the computer that is just the same as other voices.) Ideally the noise sample should be at least 5 seconds duration - more is better,
  3. Adjust the “Noise reduction (dB)” to achieve the best trade-off between lower noise and remaining sound quality (use the “Preview” button, or test on a short section before applying for real).

The other controls allow “fine tuning” of the effect, but in most cases the defaults are about right.
The default settings can be seen in the manual:

For some types of noise, other methods will sometimes work better. For example, constant hums or whistles can often be removed using the Notch Filter.

Hiss or white noise in particular is almost impossible to remove. When you get the profile, Audacity tries to build filters to remove the noise from the show. Since hiss has a little bit of all frequencies, Noise Reduction tries to remove the whole show.

Frequency Smoothing is a trick to try and get around that. That setting tries to find places where you’re speaking and stop noise reduction during those times. It noise reduces between words and leaves words largely intact, but if the noise is loud enough, it can give you hissy words.

Noise Removal is not a gift from the angels. There are posters that built a noisy show based on noise removal converting it to a studio recording.

Not so far. The best way is to identify the sources of noise and remove them before you press Record.


One trick I use is, zoom in three or four times, then select a second or two at the very end, past where the waveform ends. Then select Generate>Noise. Select as Noise type “White.” Try to match the amplitude as closely as possible to the noise in your recording, I usually never go above .001 or .002, but yours might be different. Click OK. Then get your noise profile from the selected area where you just generated the white noise. After you have the noise profile, select the whole track and run the noise removal effect. Leave Sensitivity at zero if at all possible. Moving it too far to the right is what really messes up the parts of the audio you don’t want messed up. You can use “Preview” to see what it sounds like. If you still hear noise, move “Noise reduction” to the right until you no longer hear noise.