NAME

genasa - generate auditory spectral analysis

CONTENTS

Synopsis
Description
I. Display Defaults
Iii. Leaky Integration
References
Files
See Also
Bugs
Copyright
Acknowledgements

genasa [ option=value | -option ] [ filename ]

The genasa module of the AIM software performs a time-domain spectralanalysis on the input wave using a bank of auditory filters, andsummarises the information in a sequence of auditory spectra. Thespectral analysis converts the input wave into an array of filteredwaves, one for each channel of the filterbank. The surface of thearray of filtered waves is AIM’s representation of basilar membranemotion (BMM) as a function of time (Patterson et al. 1995). Thesequence of auditory spectra is produced by calculating the envelopeof the BMM and extracting spectral slices from the envelope everyrectifing, compressing, and lowpass filtering the individual BMM wavesas they flow from the filterbank (Patterson et al. 1992a, 1993a,Patterson, 1994a).

The auditory spectrum produced by genasa is intended to simulate thespectral representation of a sound as it occurs in the peripheralauditory system just prior to neural transduction. As a result, thefrequency resolution of the analysis varies with the center frequencyof the channel, and the distribution of channels across frequency ischosen to match that in the auditory system (Patterson and Moore,1986; Glasberg and Moore, 1990). The auditory spectrum is a plot ofthe activity in each channel as a function of the centre frequency ofthe auditory filter (in ERB’s). The representation is referred to asan auditory spectrum to distinguish it from the Fourier energyspectrum (Patterson, 1994a). The suffix ’asa’ is short for ’auditoryspectral analysis’; it is used to distinguish this spectralrepresentation from three other spectral representations provided bythe AIM software (’epn’ excitation pattern, ’sgm’ auditoryspectrogram, and ’cgm’ cochleogram).

The spectral analysis performed by genasa is the same as thatperformed by genbmm. The primary differences are in the defaults forthe Displays, the Compression and the Leaky Integration used toconstruct the spectral slices from the BMM. As a result, this manualentry is restricted to describing the options that differ fromthose in genbmm.

The default values for three of the display options are reset toproduce a spectral format rather than a landscape; specifically,display=excitation, bottom=0 and top=2500. The number of channels isincreased to 128 to ensure reasonable frequency resolution in thespectral display.

The adaptive thresholding process begins with rectification andcompression of the BMM. The default form of compression islogarithmic; it has the advantage of transforming the exponentialenvelope of the ringing response of the gammatone filter into a lineardecay with time. There is evidence, however, that auditorycompression may be better represented by power compression with anexponent in the range of 0.5. It is also advisable to insert powercompression before the Meddis haircell when driving it with agammatone filter. For a discussion of these issues, seedocs/aimMeddisHewitt. To accommodate power compression and theassembly of different configurations of AIM, the rectification andcompression options are presented separately in the options listbefore the neural transduction section.

transduction	Neural transduction switch (at, meddis, off)Switch. Default: off.

stages_idt	Number of stages of lowpass filteringDefault unit: scalar. Default value: 2
tup_idt	The time constant for each filter stageDefault unit: ms. Default value: 8 ms. The Equivalent Rectandular Duration (ERD) of a two stage lowpassfilter is about 1.6 times the time constant of each stage, or12.8 ms in the current case.
downsample	The time between successive spectral frames.Default unit: ms. Default value: 10 ms. Downsample is simply another name for frstep_epn, provided tofacilitate a different mode of thinking about time-series data.
frstep_epn	The time between successive spectral framesDefault unit: ms. Default value: 10 ms. With a frstep_epn of 10 ms, genasa will producespectral frames at a rate of 100 per second.

Glasberg, B. R. and B. C. J. Moore (1990).
	"Derivation of auditory filter shapes from notched-noise data."Hearing Research, 47, 103-138.

FILES

.genasarc	The options file for genasa.

genbmm, gensgm

None currently known.

Copyright (c) Applied Psychology Unit, Medical Research Council, 1995

Permission to use, copy, modify, and distribute this software without feeis hereby granted for research purposes, provided that this copyrightnotice appears in all copies and in all supporting documentation, and thatthe software is not redistributed for any fee (except for a nominalshipping charge). Anyone wanting to incorporate all or part of thissoftware in a commercial product must obtain a license from the MedicalResearch Council.

The MRC makes no representations about the suitability of thissoftware for any purpose. It is provided "as is" without express orimplied warranty.

THE MRC DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE, INCLUDINGALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO EVENT SHALLTHE A.P.U. BE LIABLE FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGESOR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS,WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION,ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THISSOFTWARE.

The AIM software was developed for Unix workstations by JohnHoldsworth and Mike Allerhand of the MRC APU, under the direction ofRoy Patterson. The physiological version of AIM was developed byChristian Giguere. The options handler is by Paul Manson. The revisedSAI module is by Jay Datta. Michael Akeroyd extended the postscriptfacilites and developed the xreview routine for auditory imagecartoons.

The project was supported by the MRC and grants from the U.K. DefenseResearch Agency, Farnborough (Research Contract 2239); the EEC EspritBR Porgramme, Project ACTS (3207); and the U.K. Hearing Research Trust.