Audacity  2.2.0
EffectNoiseRemoval Class Reference

A two-pass effect to remove background noise. More...

Detailed Description

A two-pass effect to remove background noise.

The first pass is done over just noise. For each windowed sample of the sound, we take a FFT and then statistics are tabulated for each frequency band - specifically the maximum level achieved by at least (n) sampling windows in a row, for various values of (n).

During the noise removal phase, we start by setting a gain control for each frequency band such that if the sound has exceeded the previously-determined threshold, the gain is set to 0, otherwise the gain is set lower (e.g. -18 dB), to suppress the noise. Then frequency-smoothing is applied so that a single frequency is never suppressed or boosted in isolation, and then time-smoothing is applied so that the gain for each frequency band moves slowly. Lookahead is employed; this effect is not designed for real-time but if it were, there would be a significant delay.

The gain controls are applied to the complex FFT of the signal, and then the inverse FFT is applied, followed by a Hanning window; the output signal is then pieced together using overlap/add of half the window size.


The documentation for this class was generated from the following file: