Audio sampling (time data) is converted to a frequency spectrum using FFT (Fast Fourier Transform). Since the reference contains only the background noise while the rest of the clip contains noise + audio to clean up, you get separate frequencies so you can subtract them to get the clean audio only. Set the Denoise Power dial in dB and choose the number of reference samples.

For example, if you record a voice with a microphone3:

  1. You record 15 seconds of background (without talking). This is represent the background noise that the filter uses as a reference.
  2. After 15 seconds, start the voice. This is represents the recording whose filter should remove the background noise.
  3. You stop recording.
  4. You place the FFT effect on the whole length of the recording (including the 15 seconds of background noise).
  5. Then place your cursor at the beginning of the 15 seconds. Enter the number of samples in the effect presets, e.g. 65536.

This has the effect of creating a keyframe that marks the beginning of the reference range, mentioned in point 1, which in our example ends at 65536 samples later.

During playback, the background noise is then automatically removed along the entire length of the effect.


... microphone3
credit fary54
The CINELERRA-GG Community, 2021