NAME

gensgm - generate auditory spectrogram

CONTENTS

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

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

The gensgm module of the AIM software performs a time-domain spectralanalysis using a bank of auditory filters, and summarises theinformation in an auditory spectrogram, that is, a spectrogram withauditory frequency resolution and temporal resolution, rather than thefixed frequency and temporal resolution of traditional speechpreprocessors (Patterson and Moore, 1986; Glasberg and Moore, 1990).The spectral analysis converts the input wave into an array offiltered waves, one for each channel of the auditory filterbank. Thesurface of the array of filtered waves is AIM’s representation ofbasilar membrane motion (BMM) as a function of time (Patterson etal. 1995). The auditory spectrogram is a plot of a sequence ofspectral slices extracted from the envelope of the BMM everycalculated continuously, by rectifing, compressing, and lowpassfiltering the individual BMM waves as they flow from the filterbank.

The frequency resolution of the analysis varies with the centerfrequency of the channel as in the auditory system, and thedistribution of channels across frequency is chosen to match that inthe auditory system (Patterson and Moore, 1986). Thus, the auditoryspectrogram is a greyscale plot of the activity in each channel(shades of black) as a function of time (the abscissa) and the centrefrequency of the auditory filter (the ordinate) in ERB’s. Therepresentation is referred to as an auditory spectrogram (SGM) todistinguish it from more traditional spectrograms based on Fourier,LPC or cepstral analysis. In AIM, the suffix ’sgm’ is used todistinguish this spectral representation from the other spectralrepresentations provided by the software (’asa’ auditory spectralanalysis, ’cgm’ cochleogram, and ’epn’ excitation pattern).

The spectral analysis performed by gensgm is the same as thatperformed by genbmm. The primary differences are inthe Display defaults and the way the LeakyIntegration module is used to produce the spectral slices that form thespectrogram. As a result, this manual entry is restricted todescribing the option values that differ from those in genbmm.

The default values for three of the display options are reset toproduce a spectrographic format rather than a landscape. Specifically,display=greyscale, bottom=0 and top=2500. The number of channels isset to 128 for compatibility with the auditory spectrum modules,genasa and genepn. When using AIM as a preprocessor for speechrecognition the number of channels would typically be reduced tobetween 24 and 32. Use option ’downsample’ if it is necessary toreduce the output to less than 24 channels across the speech range.

The default form of compression is logarithmic; it has the advantageof transforming the exponential envelope of the ringing response ofthe gammatone filter into a linear decay with time. It also makes theoutput close to level independant which is useful when using AIM as apreprocessor for speech recognition. There is evidence, however, thatauditory compression may be better represented by power compressionwith an exponent in the range of 0.5. For a discussion of thisissue, see docs/aimMeddisHewitt. To accommodate power compressionand the assembly of different configurations of AIM, the rectificationand compression 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

.gensgmrc	The options file for gensgm.

genasa, genbmm, genepn, gencgm

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.