The "Noise Reduction" feature filters out noise and hiss in audio material. It works best when the noise in your material is always present at the same frequency range.
To remove brief instances of noise (e.g. crackling on vinyl recordings), use the "Crackle Removal Tool" plug-in instead.
If your audio material contains different types of noise, you can create a "noiseprint" for each one.
The "Noise Reduction Package" contains the "Vinyl Restoration" and "Click and Pop Removal" plug-ins.
Both plug-ins are suitable for restoring vinyl recordings.

• Import the audio file containing the noise.
• Select a range in the audio material which contains nothing but the noise.

The selected range does not need to be as large as the one in the picture. A one-second range is normally large enough.

• Go to "Tools" > "Noise Reduction". 
• Place a check mark next to "Capture noiseprint". 
  The "Capture noiseprint" checkbox is also located in the Noiseprint tab.
• Go to the "Noiseprint" tab.

• Click the "Preview" button on the right twice.
  A graphic representation of the noiseprint will appear.

• Click "OK" to close the Noise Reduction window. 
• Select the entire file by double-clicking it.
• Go back to "Tools" > "Noise Reduction". 
  The noiseprint you created before should still be there. 
  Now you can start making settings changes to get the best possible noise reduction result for your material.

Reduction Type

Don't worry if two different modes sound exactly the same.

• Mode 0: This mode tends to produce the best results. (This mode is susceptible to flange distortion and squeak artefacts.)
• Mode 1: Similar to Mode 0, but less susceptible to errors. The results may at times not be as good as with Mode 0.
• Mode 2: The standard mode for fast PCs. Removes less noise than Modes 0 and 1, but produces fewer artefacts.
• Mode 3: The least-susceptible mode for artefacts. Removes less noise than the other modes. Sounds the most natural out of all the modes.

Reduce Noise By

This feature specifies how much noise you want to remove.
The higher the value, the more noise is removed.
Values between 10db and 20db typically produce the best results.

Noise Bias

This feature can make a big difference in the quality of the results you get (fewer artefacts).

Attack Speed

This value determines how quickly the algorithm responds to a signal without any noise.
You typically will not need to change this value.
If you are using a very high FFT value, then the attack speed also needs to be higher.

Release Speed

This value determines how quickly the algorithm responds to a signal with noise.
You typically will not need to change this value.
If you are using a very high FFT value, then the release speed also needs to be higher.

Windowing FFT Size

This value shows the size of the samples used by the algorithm to analyze the frequency spectrum.

Windowing Overlap

This value shows how much overlap there is between the frequency analysis windows.
Overlap can sometimes result in more accurate analysis.

High-Shelf Filter

The high-shelf filter is used to brighten up the sound after the noise reduction is performed.
Noise reduction removes higher frequencies from your source material.
Turning the high-shelf filter on helps lessen this effect.
To enable this feature, place a check mark next to it.

• High-Shelf Start Freq: This value defines the frequency at which the filter becomes active.
• High-Shelf Gain: Defines the decibel range in which the filter becomes active.

Keep Residual Output

Enabling this feature causes the Noise Reduction feature to become inverted.
Everything that is normally removed by the Noise Reduction feature is instead kept.
And what you hear is the noise that should be removed.