critical band vocoder

["Eric W. Healy" <ewh@xxxxxx>]

Jim,

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,

-Eric

> 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