[Speex-dev] Preprocessor denoise. Does it work?

Andy Ross andy at plausible.org
Tue Feb 27 14:38:12 PST 2007

I'm having trouble with the preprocessor's noise reduction feature.
The basic issue is that it simply doesn't work very well.

With my laptop (whose microphone is otherwise quite capable) I
routinely hear transient background noise, typing, and other "quiet"
sounds leaking through to the speex stream.  Even worse, the AGC
feature is blowing these things up into just awful explosions and

Honestly, it works so badly that I wonder if I'm doing something
wrong.  I wrote a trivial squelch feature* in 10 minutes that works
basically 100% of the time.

* Zero the sample data if the maximum sample in a frame is less than
  4% of saturation or 20% of the maximum sample yet seen.  It's about
  8 lines of code.

I'm using the 32KHz ultra wide band mode with 16 bit sample data and
am setting all of AGC, VAD, DEREVERB and DENOISE to 1 using
speex_preprocess_ctl().  AGC_LEVEL is set to 20000.0.

Any thoughts?


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