There are two ways of reducing noise. The slow but accurate "Spectral Subtraction" method - usually used where noise is really a problem - and the fast "Multiband Noise Gates" method - usually just automatically on batch voice recording jobs.

Sometimes using both (spectral always must be first) then multiband gates works very well.

Spectral Subtraction
Automatic Method
This approach will automatically estimate what is noise and what is not. It usually works well on voice and is nice and easy to use; just select the region and apply the effect.
Manual Method
To use this you must:
  1. Select a short part of 'noise only'. Usually this is from a gap in the audio.
  2. Select Effects -> CleanUp -> Noise Reduction -> "Grab noise sample from selected area for spectral subtraction".
  3. Select the entire file.
  4. Select Effects -> CleanUp -> Noise Reduction -> "Spectral subtraction based on noise sample".
Multi-Band Noise Gate
Multi-Band Noise Gate removes all the audio data below a given threshold in the audio file. A good noise threshold for most audio files is usually between -30dB and -20dB.

Noise Gate

A noise gate is a filter which controls the volume of an audio signal. Any part of your audio which is below the Threshold will be attenuated by the amount you specify.

Audio falling below this threshold will be attenuated.
The period of time (in milliseconds) to wait before applying the attenuation.
The period of time (in milliseconds) taken to fully apply the attenuation.
The period of time (in milliseconds) taken to fully remove the attenuation.
The amount to attenuate the audio signal when it falls below the threshold.

Noise Removal Wizard

An easy-to-use noise removal wizard can be found on the Tools tab. The wizard guides you through choosing the best parameters based on noise type description, then applies the noise reduction. To use the wizard, click the Noise Removal button on the Tools tab.