view man/man1/gencgm.1 @ 0:5242703e91d3 tip

Initial checkin for AIM92 aimR8.2 (last updated May 1997).

.TH GENCGM 1 "11 May 1995" 
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.SH NAME 
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gencgm \- generate a cochleogram 
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.SH SYNOPSIS 
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gencgm [ option=value | -option ] [ filename ] 
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.SH DESCRIPTION 
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Gencgm converts the input wave into a simulated neural activity
pattern (NAP) and summarises the NAP as a sequence of excitation
patterns (EPNs) that collectively form a 'cochleogram' (CGM). The
operation takes place in three stages: spectral analysis, neural
encoding, and temporal integration. In the spectral analysis stage,
the input wave is converted into an array of filtered waves, one for
each channel of a gammatone auditory filterbank. The surface of the
array of filtered waves is AIM's representation of basilar membrane
motion (BMM) as a function of time (manaim genbmm). In the neural
encoding stage, compression, adaptation and suppression, are used to
convert each wave from the filterbank into a simulation of the
aggregate neural response to that wave. The array of responses is
AIM's simulation of the neural activity pattern (NAP) in the auditory
nerve at about the level of the cochlear nucleus (manaim gennap).
Finally, the NAP is converted into a sequence of excitation patterns
(EPNs) by calculating the envelope of the NAP and extracting spectral
slices from the envelope every 'frstep_epn' ms. The envelope is
calculated continuously, by lowpass filtering the individual channels
of the NAP as they flow from the cochlea simulation.  
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When the sequence of excitation patterns is presented in spectrogram
format, it is referred to as a 'cochleogram' (CGM). The spectrogram
format has time on the abscissa (x-axis), filter centre-frequency on
the ordinate (y-axis), and activity level as the degree of black in
the display.  In AIM, the suffix 'cgm' is used to distinguish this
spectral representation from the other spectral representations
provided by the software ('asa' auditory spectral analysis, 'sgm'
auditory spectrogram, and 'epn' excitation pattern).
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The NAP generated by gencgm is the same as that produced by gennap
(manaim gennap).  The primary differences are in the display defaults
and the inclusion of the Leaky Integration used to construct the
excitation patterns that form the cochleogram.  As a result, this
manual entry is restricted to describing the option values that differ
from those in gennap and the additional options required to control
the Leaky Integration.
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.SH DISPLAY DEFAULTS
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The default values for three of the display options are reset to
produce a spectrographic format rather than a landscape. Specifically,
display=greyscale, bottom=0 and top=2500. The number of channels is
set to 128 for compatibility with the auditory spectrum modules,
genasa and genepn.  When using AIM as a preprocessor for speech
recognition the number of channels would typically be reduced to
between 24 and 32.  Use option 'downsample' if it is necessary to
reduce the output to less than 24 channels across the speech range.
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.SH COMPRESSION AND LEAKY INTEGRATION
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Compression and lowpass filtering are activated after the neural
encoding stage:
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.SS "Compression"
.PP
Cochleograms are usually produced via the functional route in AIM. In
this case, compress is set on
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.TP 13
compress
Logarithmic compressor switch
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Switch. Default: on.
.RE
.RS
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Note: The compressor in the functional route of AIM is logarithmic and
it screens out negative BMM values before compression. This rectifies
the wave during the compression process and so the separate rectify
option is left off. 
.RE
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.RS
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Note: The compressor in the physiological route of AIM is an integral
part of the tlf module, so when using this route to produce a
cochleogram, turn off the logarithmic compressor
(i.e. compress=off). The compressor in tlf does not screen out
negative values so it is also important to set rectify=on.
.RE
.RS
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Full wave rectification is produced if rectify is set to 2. This will
lead to a smoother cochleogram from both the physiological and the
functional versions of AIM.
.RE
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.SS "Transduction"
.PP
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transduction
Neural transduction switch (at, meddis, off)
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Switch. Default: at.

.RE
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.SS "Leaky Integration"
.PP
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stages_idt
Number of stages of lowpass filtering
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Default unit: scalar. Default value: 2
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tup_idt
The time constant for each filter stage
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Default unit: ms. Default value: 8 ms.
.RE
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The Equivalent Rectandular Duration (ERD) of a two stage lowpass
filter is about 1.6 times the time constant of each stage, or
12.8 ms in the current case.
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frstep_epn
The time between successive spectral frames
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Default unit: ms. Default value: 10 ms.
.RE
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With a frstep_epn of 10 ms, gencgm will produce spectral frames at a
rate of 100 per second.
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downsample
The time between successive spectral frames. 
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Default unit: ms. Default value: 10 ms.
.RE
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Downsample is simply another name for frstep_epn, provided to
facilitate a different mode of thinking about time-series data.
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.SH FILES
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.TP 13
.gencgmrc 
The options file for gencgm.
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.SH SEE ALSO
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gensgm, genasa, genepn, gennap, genbmm
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.SH BUGS
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None currently known.
.SH COPYRIGHT
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Copyright (c) Applied Psychology Unit, Medical Research Council, 1995
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Permission to use, copy, modify, and distribute this software without fee 
is hereby granted for research purposes, provided that this copyright 
notice appears in all copies and in all supporting documentation, and that 
the software is not redistributed for any fee (except for a nominal 
shipping charge). Anyone wanting to incorporate all or part of this 
software in a commercial product must obtain a license from the Medical 
Research Council.
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The MRC makes no representations about the suitability of this 
software for any purpose.  It is provided "as is" without express or 
implied warranty.
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THE MRC DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE, INCLUDING 
ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO EVENT SHALL 
THE A.P.U. BE LIABLE FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES 
OR 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 THIS 
SOFTWARE.
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.SH ACKNOWLEDGEMENTS
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The AIM software was developed for Unix workstations by John
Holdsworth and Mike Allerhand of the MRC APU, under the direction of
Roy Patterson. The physiological version of AIM was developed by
Christian Giguere. The options handler is by Paul Manson. The revised
SAI module is by Jay Datta. Michael Akeroyd extended the postscript
facilites and developed the xreview routine for auditory image
cartoons.
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The project was supported by the MRC and grants from the U.K. Defense
Research Agency, Farnborough (Research Contract 2239); the EEC Esprit
BR Porgramme, Project ACTS (3207); and the U.K. Hearing Research Trust.