Noise reduction & removal
Removing background noise is core to most audio cleanup operations. Audacity has several tools to aid in this.
Best Practice: While it's possible to rescue an otherwise unusable file with noise reduction techniques, your recording will sound best if you take steps to ensure a noise-free environment before recording.
The Noise Reduction effect works best to remove a constant source of noise, like the hiss of fans, the hum of fridges, or whines, whistles and buzzes.
To use it, use the following steps:
- 1.Locate a section of your recording that's just your background noise, preferably a few seconds long, and select it.
- 2.Go to Effects > Noise Reduction and press the "Get noise profile" button.
- 3.Select all the audio for which you want to reduce the noise.
- 4.Go to Effects > Noise Reduction again. You now can tweak the settings of the reduction to your liking. Tip: While tuning the settings, use the "Residue" toggle to hear what sound will be removed.
- 5.Once you're satisfied with the result, click OK to apply it to the selected audio. Note: If you used the Residue toggle before, make sure to switch it back to Reduce before pressing OK.
- If you set the sensitivity too low, or use a noise profile that doesn't properly represent the noise throughout your track, you may experience artifacts (random bursts of very short tones).
- If you don't need to tweak the settings after setting the noise profile, you can press
Cmd+Rto immediately apply the effect to your selection.
The Noise Gate effect attenuates any sound quieter than a certain threshold while leaving sounds louder completely unaffected. To use it
- 1.Select a part of the audio that's just background noise.
- 2.Go to Effects > Noise Gate... to open the effect.
- 3.Click Select Function: Analyse Noise Level and press OK. Audacity will now tell you where your noise level lies and recommending a threshold.
- 4.Select the audio you want to apply the effect to.
- 5.Go back into Effects > Noise Gate..., set it back to Select Function: Gate, and enter the threshold level from earlier.
- 6.Tweak the other parameters as sound best to you.
- 7.Press OK to apply the noise gate.
Best practice: Use the noise gate after applying noise reduction. This way, you can use less aggressive noise reduction settings, which may grant you a cleaner end result.
The notch filter removes a hum or whistle at a specific frequency. To use it:
- 1.Select the audio you want to apply the effect on
- 2.Go to Effects > Notch Filter to open the effect.
- 3.Enter the frequency you want to reduce, together with the Q-value (how many frequencies around the main one you want it to affect - the higher the number, the less frequencies).
- 4.Press OK to apply the effect.
- The "Mains hum" of the electricity grid is 60Hz in north and middle America, and 50Hz in most other countries.
- Use Analyze > Plot Spectrum... to find the offending frequency if you're not sure where it is.
- Sounds often have harmonics or overtones. They are at a multiple of the main frequency, so for a 50Hz sound, you may need to apply the notch filter as well at 100Hz, 150Hz, and so on to remove it fully.