dnoise

Name

dnoise --  Reduces noise in a file.

Description

This is a noise reduction scheme using frequency-domain noise-gating.

Syntax

dnoise [flags] -i noise_ref_file  -o output_soundfile  input_soundfile

Initialization

Dnoise specific flags:

Soundfile format options:

Additional options:

Note: DNOISE also looks at the environment variable SFOUTYP to determine soundfile output format.

The -i flag is used for a reference noise file (normally created from a short section of the denoised file, where only noise is audible). The input soundfile to be denoised can be given anywhere on the command line, without a flag.

Performance

This is a noise reduction scheme using frequency-domain noise-gating. This should work best in the case of high signal-to-noise with hiss-type noise.

The algorithm is that suggested by Moorer & Berger in "Linear-Phase Bandsplitting: Theory and Applications" presented at the 76th Convention 1984 October 8-11 New York of the Audio Engineering Society (preprint #2132) except that it uses the Weighted Overlap-Add formulation for short-time Fourier analysis-synthesis in place of the recursive formulation suggested by Moorer & Berger. The gain in each frequency bin is computed independently according to

gain = g0 + (1-g0) * [avg / (avg + th*th*nref)] ˆ sh
      

where avg and nref are the mean squared signal and noise respectively for the bin in question. (This is slightly different than in Moorer & Berger.)

The critical parameters th and g0 are specified in dB and internally converted to decimal values. The nref values are computed at the start of the program on the basis of a noise_soundfile (specified in the command line) which contains noise without signal.

The avg values are computed over a rectangular window of m FFT frames looking both ahead and behind the current time. This corresponds to a temporal extent of m*D/R (which is typically (m*N/8)/R). The default settings of N, M, and D should be appropriate for most uses. A higher sample rate than 16 Khz might indicate a higher N.

Credits

Author: Mark Dolson

August 26, 1989

Author: John ffitch

December 30, 2000

Updated by Rasmus Ekman on March 11, 2002.