Re: Rationale for Critical Bands (Christine Rankovic )


Subject: Re: Rationale for Critical Bands
From:    Christine Rankovic  <rankovic@xxxxxxxx>
Date:    Tue, 15 Jun 2010 16:46:15 -0400
List-Archive:<http://lists.mcgill.ca/scripts/wa.exe?LIST=AUDITORY>

Dear List: Regarding Brian's comment on speech intelligibility at high intensities: In his version of the articulation index, Fletcher did not increase the width of the auditory filter to account for the reduction in speech intelligibility in quiet observed at high intensity levels, a phenomenon often referred to as "rollover." Fletcher attributed rollover to a combination of self-masking of speech by both simultaneous (masking spread) and forward (within band) masking, and to ear-generated distortion products which may arise in conditions such as, for example, under high-frequency amplification. Fletcher incorporated methods for calculation these effects into his definitive 1950 version of the articulation index calculation published with R. Galt in JASA (this is the same calculation as in Fletcher's 1953 book). Fletcher was the first to describe the critical band concept and determine the bandwidths experimentally, so I'm convinced that his decision not to broaden the auditory filter was an informed one. In fact, he oversaw Bell Labs researchers French and Steinberg, whose 1947 version of the articulation index (a simplified AI calculation developed for military applications) included a factor, m, that effectively broadened the filters to account for excess masking at high intensities. References: H. Fletcher, Speech in Hearing in Communication (1953). Van Nostrand, New York. (or ASA edition available at asa.aip.org). H. Fletcher, and R.H. Galt (1950). Journal of the Acoustical Society of America vol. 22, 89-151. H. Fletcher and W.A. Munson (1933). Journal of the Acoustical Society of America vol. 5, 82-108 for original critical band discussion. N.R. French and J.C. Steinberg (1947). Journal of the Acoustical Society of America vol. 19, 90-119. Christine Rankovic, PhD Research Scientist Articulation Inc 94 Berkshire Road Newton, MA 02460 USA -----Original Message----- From: AUDITORY - Research in Auditory Perception [mailto:AUDITORY@xxxxxxxx On Behalf Of Brian C. J. Moore Sent: Tuesday, June 15, 2010 10:42 AM To: AUDITORY@xxxxxxxx Subject: Re: Rationale for Critical Bands Dear All At 15:00 15/06/2010, Wiebe Horst wrote: >Dear all, > >I am getting more and more confused by this discussion. >It would help if every contributor started by giving his/her >definition of Critical Band. >I am used to using Scharf's (1970) definition: >"The critical band is a band of that width at which subjective >responses change rather abruptly." The problem with this definition is that there are few if any auditory responses which "change rather abruptly" at a certain bandwidth. The perceptual changes are nearly always smooth and progressive, consistent with auditory filters with rounded tops. And speech perception does deteriorate at high levels, probably due to broadening of the auditory filters. See, for example: Studebaker, G. A., Sherbecoe, R. L., McDaniel, D. M., Gwaltney, C. A., 1999. Monosyllabic word recognition at higher-than-normal speech and noise levels. J. Acoust. Soc. Am. 105, 2431-2444. Best wishes, Brian Moore Brian C. J. Moore, Ph.D, FMedSci, FRS, Professor of Auditory Perception, Department of Experimental Psychology, University of Cambridge, Downing Street, Cambridge CB2 3EB, UK Tel. +44 (0) 1223 333574 Fax. +44 (0) 1223 333564 http://hearing.psychol.cam.ac.uk


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