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critical band vocoder


Yes, recent efforts have shifted toward partitioning the spectrum in "appropriate" ways.

We used critical-band divisions to assess frequency resolution in restricted regions of the spectrum.
Healy & Bacon (2006). Measuring the critical band for speech. JASA, 119, 1083-1091.

Also, equal distance along the BM (Greenwood's 1990 formula) can be considered a good representation of CIs.
Faulkner, Rosen, & Smith (2000, JASA, vol. 108, pp. 1877-1887)
Fu, Chinchilla, & Galvin (2004, JARO, vol. 5, pp. 253-260)
Xu, Thompson & Pfingst (2005, JASA, vol. 117, pp. 3255-3267)

There are other authors that have used these divisions and other division methods as well.

However, as Shannon and his colleagues showed, vocoded broadband speech is robust and, so long as analysis (speech) bands match presentation (noise) bands, performance differences resulting from different frequency divisions (linear, log [Greenwood], "standard" ) are small.
Shannon, Zeng, & Wygonski (1998, JASA, vol. 104, pp. 2467-2476).

Hope this helps,


Date:         Wed, 17 May 2006 15:07:02 -0500
From: beaucham <beaucham@xxxxxxxxxxxxxxxxxxxxxx>
Subject: critical band vocoder
To: AUDITORY@xxxxxxxxxxxxxxx

For many years vocoders were used for data reduction of speech signals.
A vocoder separates the input signal into consecutive bands, codes the
band outputs, and then transmits the coded information to a receiver
for resynthesis. An early model of Bell Lab's vocoder used 20
uniform-width bands below 3000 Hz and 10 log-spaced bands above 3000
Hz, extending to 7500 Hz.

Recently, mel-frequency cepstral coefficients have been popular for
speech recognition. Mel frequency spacing is approximately proportional
to critical-band frequency spacing. My question is: Has anyone designed
and tested a vocoder using critical-band spacing of the filters?

Jim Beauchamp
Univ. of Illinois at Urbana-Champaign

Eric W. Healy, Ph.D.
Assistant Professor
Department of Communication Sciences and Disorders
Arnold School of Public Health
University of South Carolina
Columbia, SC 29208
(803) 777-1087 voice (803) 777-3081 fax