comparison man/man1/genbmm.1 @ 0:5242703e91d3 tip

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

+.TH GENBMM 1 "11 April 1994"
+.LP
+.SH NAME
+.LP
+genbmm \- generate basilar membrane motion
+.LP
+.SH SYNOPSIS
+.LP
+genbmm [ option=value | -option ] [ filename ]
+.LP
+.SH DESCRIPTION
+.LP
+The genbmm module of the AIM software simulates the spectral analysis
+performed by the auditory system using a bank of auditory filters.
+Specifically, genbmm converts an input wave into an array of filtered
+waves, one for each channel of the filterbank. The surface of the
+array of filtered waves is AIM's representation of basilar membrane
+motion (BMM) as a function of time.  AIM provides two alternative
+methods for generating the BMM, linear, gammatone filterbank
+(Patterson et al, 1988; Slaney 1993, Cooke, 1993), or a nonlinear,
+transmission-line filterbank (Giguere and Woodland, 1994). For
+convenience, they are referred to as the 'functional' filterbank and
+the 'physiological' filterbank, respectively.
+.LP
+.SH OPTIONS
+.LP
+There are three sets of options for genbmm; they are grouped by
+function and identified by the suffixes _afb, _gtf and _tlf. The first
+set controls the distribution of the filtered waves across frequency
+(suffix _afb); the second specifies the shape of the gammatone filter
+(suffix _gtf); and the third specifies the shape of the transmission
+line filter (suffix _tlf). These three groups of options are the
+subject of this manual entry, together with an option that specifies
+the filter choice (gtf or tlf), and an option that specifies whether a
+middle ear function should be used with the gtf filterbank.
+.LP
+.SS "The Outer/Middle Ear function: middle_ear "
+.PP
+In the auditory system the middle ear causes a progressive attenuation
+of sound energy in the region below about 500 Hz and a progressive
+attenuation in the region above about 4000 Hz.  There is also a
+primary auditory canal resonance around 2700 Hz that provides a boost
+in sound transmission. The resulting transfer function is a normal
+aspect of auditory processing and preceeds spectral analysis. If the
+functional filterbank is chosen (gtf), the outer/middle ear filter
+acts directly on the input wave, and the stapes velocity wave it
+generates is the input to the spectral filtering stage. If the
+physiological filterbank is chosen (tlf), the outer/middle ear and
+cochlear filter are performed simultaneously as in the auditory
+system. The only parameter associated with this function is the
+middle_ear switch which makes it possible to turn the outer/middle ear
+filtering off when the functional filterbank is chosen.
+.LP
+.TP 13
+middle_ear
+Outer/middle ear switch
+.RS
+Switch. Default: on. 
+.RE
+.RS
+.LP
+It is also possible to specify a floating point number, in which 
+case the middle ear output is multiplied by that value.
+.RE
+.LP
+Note: The middle_ear option is ignored if option filter (see below) 
+is set to tlf. This is because the outer/middle stage and the 
+cochlear stage are bidirectionally coupled in the transmission 
+line filter implementation, and cannot be separated. 
+.RE
+.LP
+.SS "The Auditory FilterBank options: _afb "
+.PP
+The distribution of the filters across frequency and the total 
+number of output filters in the bank are determined by four parameters: 
+channels_afb, mincf_afb, maxcf_afb, and dencf_afb. 
+.LP
+.TP 13
+channels_afb
+The number of channels in the filterbank. 
+.RS
+Default unit: filters. Default value: 75 
+.RE
+.TP 13
+mincf_afb
+The minimum centre frequency 
+.RS
+Default unit: Hz. Default value: 100 Hz. 
+.RE
+.TP 13
+maxcf_afb
+The maximum centre frequency 
+.RS
+Default unit: Hz. Default value: 6000 Hz. 
+.RE
+.TP 13
+dencf_afb
+The density of the filters in the filterbank. 
+.RS
+Units: filters/critical band. Default: off 
+.RE
+.RS
+.LP
+dencf_afb provides an alternative method of specifying the number of channels 
+in terms of the density of filters along the frequency scale. 
+.RE
+.LP
+Note: channels_afb overrides dencf_afb whenever it has a non-zero 
+value.  The values of dencf_afb and channels_afb may conflict at 
+this point, in which case dencf_afb is ignored.
+.RE
+.LP
+WARNING: When using the transmission line filter (filter=tlf), the
+channel density should be 3 or more filters/erb.  Using a lower
+density may lead to excessive spatial discretization errors (see
+Giguere and Woodland (1994) for a discussion).  To view a small number
+of channels, use a reasonable density and reduce the number of
+displayed channels using option downchannel.
+.LP
+.TP 14
+audiogram_afb
+The audiogram 
+.RS
+Units: none. Default: off. Status: obsolete.
+.RE
+.LP
+Note: In the versions up to and including AIM R6.15, this parameter
+was used as a means of approximating equal loudness contours, as well
+as middle ear attenuation. It applies a spectral weighting function at
+the output of the filterbank. With the addition of the outer/middle
+ear transfer function, this parameter is obsolete, and so the default
+value is off. Users who wish to use the audiogram parameter instead of
+the new outer/middle filter as a loudness equilisation function can
+still do so by setting audiogram_afb=on and middle_ear=off. As before,
+audiogram_afb is applied as a power function and so as the value of
+audiogram_afb decreases from 1 to 0, the degree of attenuation
+decreases.  Values greater than unity are allowed but their
+interpretation is unclear.
+.RE
+.LP
+The ERB scale for the gammatone auditory filterbank
+is specificed with three options: bwmin_afb, quality_afb, 
+and mmerb_afb. 
+.LP
+.TP 13
+bwmin_afb
+The minimum bandwidth for an auditory filter. 
+.RS
+Default unit: Hz. Default value: 24.7 
+.RE
+.TP 13
+quality_afb
+The limiting quality factor for high frequency auditory filters. 
+.RS
+Units: scalar. Default: 9.265 
+.RE
+.TP 13
+mmerb_afb
+The length of one erb-rate unit along the basilar membrane.
+.RS
+Units: mm. Default: 0.89
+.RE
+.LP 13
+A listing of the parameters for the filter in the bank can be directed
+to the terminal at run time by setting info_afb=on.
+.RE
+.TP
+info_afb
+Print filterbank information to stderr.
+Switch. Default: off.
+.RE
+.LP
+The physiological data on human cochlear frequency-position 
+function (Greenwood, 1990) and the psychoacoustic data on auditory 
+filter bandwidth (Patterson and Moore, 1986) indicate that the 
+spectral analysis performed in the cochlea is like a 'constant Q' 
+system (quality_afb) that asymptotes to a minimum filter bandwidth 
+(bwmin_afb) at low centre frequencies. That is,
+.PD 0
+.LP
+.PD 4
+.LP
+	erb = bwmin_afb + centre-frequency/quality_afb.  
+.PD 0
+.LP
+.PD 4
+.LP
+If we assume, as Greenwood suggests, that each filter bandwidth
+corresponds to a constant distance (mmerb_afb) along the basilar
+membrane, it is possible to scale frequency in terms of erb units (or
+position along the basilar membrane) by integrating the inverse of the
+erb function above.
+.RE
+.LP
+Glasberg and Moore (1990) have reviewed the available human filter
+shape data and concluded that the optimum values for bwmin_afb and
+quality_afb are 24.7 and 9.265, respectively, together with mmerb_afb
+of 0.89.  (As a rule of thumb for rapid estimation, erb = 25 + 10% of
+cf ). The auditory scale used by Greenwood (1990) can be specified by
+setting bwmin_afb=22.85, quality_afb=7.238 and mmerb_afb=1.0. A
+reasonable approximation to the Bark scale (Zwicker, 1961) is obtained
+by setting bwmin_afb=80, quality_afb=6.5 and mmerb_afb=0.89.
+.RE
+.LP
+.SS "Auditory filter design: filter "
+.PP
+The choice of filterbank -- linear gammatone or nonlinear transmission
+line -- is determined by option filter.
+.LP
+.TP 13
+filter
+The auditory filter design
+.RS
+Default: gtf. Choices: gtf, tlf, off.
+.RE
+.LP
+When gtf is specified, the options below with suffix _gtf apply, and
+when tlf is specified, the options below with suffix _tlf apply. When
+off is specified, the input wave (or the stapes velocity) is passed on
+directly to the next stage. This provides for non-auditory use of the
+modules following the filterbank with their associated displays. For
+example, the envelope of the input wave (or stapes velocity) can be
+extracted using the rectification and integration modules that follow
+genbmm. The entry point genasa has the most convenient default
+settings for this purpose. The default value for the filter option is
+gtf.
+.RE
+.LP
+.SS "The GammaTone Filter options: _gtf "
+.LP
+.TP 13
+order_gtf
+The order of the gammatone filter 
+.RS
+Units: none. Default: 4 
+.RE
+.RS
+.LP
+The order of the filter, order_gtf, determines the number of filtering
+stages and so it determines the slope of the skirts of the attenuation
+function and their extent. The default value is 4 and the range of
+useful values is from about 2 to 8.  The processing time increases
+linearly with order above about order 2.
+.RE
+.LP
+Note that the bandwidth calculation takes account of the fact that
+changes in order_gtf affect bandwidth. Thus, as long as bwmin_afb is
+fixed, changing the order will not affect the bandwidths of the
+resulting filters.  Increasing the order of the filter increases the
+delay of the onset of the impulse response but it has little effect on
+the shape of the envelope of the impulse response for orders greater
+than three. The human auditory system is not sensitive to small phase
+changes between filter channels (Patterson, 1987) and so filter order
+is not well constrained by human experimental data.  The default value
+(4) is used because this value provides the best match between the
+amplitude characteristics of the gammatone and roex filters for humans
+(Patterson et al., 1988).
+.LP
+.TP 13
+gain_gtf
+Filter output amplification 
+.RS
+Units: scalar. Default: 4.
+.RE
+.RS
+.LP
+The ratio of input to output level across the auditory filter 
+when the input is a sinusoid at the cf of the filter.
+.RE
+.TP 13
+phase_gtf
+The phase of the impulse response (obsolete)
+.RS
+Units: none. Default: 0. 
+.RE
+.LP
+In the absence of phase compensation, the surface of basilar membrane
+motion has a strong rightward skew in the low-frequency channels
+because the filters get progressively narrower as centre frequency
+decreases, and this narrowing is accompanied by a slower filter
+response. There are occassionally non-auditory reasons for wanting to
+align the channels across frequency in one way or another. The
+software provides four alignment systems which are discussed at the
+end of this entry just before the references under the title Phase
+Alignment.
+.RE
+.LP
+.SS "The Transmission Line Filter options: _tlf "
+.LP
+.TP 13
+motion_tlf
+The basilar membrane output motion variable
+.RS
+Default: vel. Choices: vel, disp.
+.RE
+.RS
+.LP
+If vel (velocity) is specified, the output of genbmm
+is the basilar membrane velocity. If disp (displacement)
+is specified, the output of genbmm is the basilar membrane
+displacement. The default value is vel.
+.RE
+.TP 13
+outdencf_tlf
+The density of the filters outside the display
+range. 
+.RS
+Units: filters/critical band. Default: 4.
+.RE
+.RS
+.LP
+In the transmission line filter implementation, it is necessary to
+simulate the basilar membrane over its entire length.  The option
+outdencf_tlf provides a means of specifying the number of additional
+channels that must be computed at the basal and apical ends of the
+cochlea, ie. outside the range specified by mincf_afb and maxcf_afb
+(see above).  These additional channels are only computed for internal
+use and are not passed to the next stage of processing.
+.RE
+.TP 13
+qref_tlf
+The local quality factor of each basilar membrane channel
+.RS
+Units: scalar. Default: 2. 
+.RE
+.RS
+.LP
+Note: With the transmission line filter, the bandwidth is not
+determined by options bwmin_afb and quality_afb at high levels but
+rather by option qref_tlf (see above).
+.RE
+.TP 13
+feedback_tlf
+The feedback gain of the outer hair cell circuit
+.RS
+Units: scalar. Default: 0.99
+.RE
+.RS
+.LP
+WARNING: A value for feedback_afb greater than or equal to 1.0 can
+lead to unstable behaviour at low-levels (ie. oscillation).  However,
+the model output will not grow unbound. The growth of the oscillations
+will be limited by the saturating nonlinearity of the outer hair cell
+circuit, and the model output will go into a kind of limit-cycle.
+These model oscillations have not yet been studied in detail and are
+likely to deviate substantially from real cochlear emissions.
+.RE
+.TP 13
+dsat_tlf
+The basilar membrane displacement at the half-saturation point 
+of the outer hair cell circuit
+.RS
+Units: cm. Default: 5.75e-6
+.RE
+.TP 13
+gain_tlf
+Filter output amplification 
+.RS
+Units: scalar. Default: 4.
+.RE
+.RS
+.LP
+Note: There is an internal gain of 4.0 within the software of
+the transmission line model itself. The total gain is therefore
+4.0 times the value for gain_tlf.
+.RE
+.LP
+Note: A linearized version of the transmission line filter with
+roughly the same bandwidth as the gammatone filter can be obtained by
+setting feedback_tlf=0 and qref_tlf to about 10.  The main difference
+is that the low-frequency skirt of the transmission line filter is
+less steep than that of the gammatone.
+.LP
+.SH FURTHER DESCRIPTION
+.LP
+.SS "The distribution of filter centres along the ERB scale. "
+.LP
+Given values for mincf_afb maxcf_afb and channels_afb (or 
+dencf_afb), the program creates an array of centre frequencies 
+in three steps:
+.LP
+1. It centres a filter at 1.0 kHz.
+.RE
+.LP
+2. Then it centres filters below 1.0 kHz, one after another, 
+until it encounters mincf_afb. (Thus, mincf_afb is actually the 
+frequency below which no filters are centred). The step size, 
+that is the distance between centre frequencies, is determined 
+by dencf_afb. When dencf_afb is equal to one, the centre 
+frequencies are 1 ERB apart. The ERB is the Equivalent 
+Rectangular Bandwidth of the filter (about 14% larger than the 3 
+dB bandwidth of the filter). The function relating the ERB to the 
+centre frequency of the filter is taken from a `critical band' 
+equation introduced by Greenwood (1961) and adapted to human 
+auditory masking by Glasberg and Moore (1990).
+.RE
+.LP
+3. Finally, the program centres filters one after another in 
+the region above 1 kHz until it encounters maxcf_afb (which is, 
+actually, the frequency above which no filters are centred). When 
+dencf_afb is increased, say to two, the program allocates two 
+filters per critical band and spaces them at half ERB steps.
+.RE
+.LP
+Note: It is not the bandwidths of the filters that are 
+controlled by dencf_afb but rather the density of filters along 
+the frequency axis. Thus, doubling dencf_afb does not cause the 
+bandwidth of the filters to be halved; rather it results in more 
+overlap between adjacent filters. With regard to the images 
+produced by genbmm, dencf_afb determines the density of lines on 
+the surface rather than the shape of the features that appear on 
+the surface.
+.LP
+.SH MOTIVATION
+.LP
+The motivation for adopting the gammatone filter shape is 
+threefold:
+.LP
+1. It provides an excellent summary of physiological data 
+concerning the impulse response of primary auditory neurons in 
+small mammals such as cats (de Boer and de Jongh, 1978; Carney and 
+Yin, 1989)
+.RE
+.LP
+2. The amplitude characteristic of the gammatone filter is very 
+similar to that of the Roex filter commonly used to represent the 
+human auditory filter (Patterson, et al, 1982; Schofield, 1985; 
+Patterson et al, 1988) .
+.RE
+.LP
+3. There are recursive gammatone filters that make the calculation
+particularly fast both on general purpose computers and special
+purpose DSP chips (Holdsworth et al, 1988; Cooke, 1993; Slaney, 1993).
+.RE
+.LP
+In summary, the gammatone filter is designed to provide a reasonable
+trade-off between accuracy in simulating basilar membrane motion, and
+computational load.
+.RE
+.LP
+The motivation for adopting the transmission line filter is 
+as follows:
+.LP
+1. The outer hair cell circuit of the transmission line filter is
+level dependent and so this design produces level-dependent basilar
+membrane tuning curves (Giguere and Woodland, 1994). There is now
+ample evidence that the basilar membrane motion is indeed highly
+nonlinear and a major source of level compression (eg. Johnstone et
+al., 1986).
+.LP
+2. The internal structure of the transmission line filter model is
+based on the physics of the auditory periphery and therefore provides
+a more realistic cochlear simulation than parallel filterbanks. It
+generates combination tones of the form 2f1-f2 as observed in the
+auditory system and it has the potential to generate cochlear echoes.
+.LP
+3. The wave-digital-filter implementation of the transmission line
+filterbank is only about twice as slow as the gammatone filterbank
+for an equivalent number of channels.
+.RE
+.LP
+.SH "Phase Alignment"
+.LP
+There is no question that the output of the cochlea has a phase lag
+corresponding to the strong rightward skew. However, perceptual
+evidence indicates that this phase lag has to be enormous (> 4ms) to
+affect what we hear; indeed, reversing the phase lag with synthetic
+stimuli does not change what we hear (Patterson, 1987).  Phase
+information that appears in the basilar membrane motion but which we
+do not hear, is removed in the third module by the strobe mechanism of
+the temporal integration process. As a result, the stabilised auditory
+images are always phase aligned even though the basilar membrane
+motion and the neural activity patterns are not.
+.RE
+.LP
+Prior to discovering the integration mechanism, we wanted to find 
+a way of reducing the skew from the basilar membrane image, in 
+order to provide a visual representation that was more like what 
+we hear. The genbmm program provides the following options for 
+phase aligning the responses of successive filters, determined 
+by the value of the option phase_gtf:
+.RE
+.LP
+Value Effect
+.PP
+.TP 7
+-1
+Envelope alignment. 
+.RS
+Shift the channels of output horizontally so that the points of 
+maximum response to an impulse (ie the envelope maxima) will be aligned. 
+.RE
+.TP 7
+-2
+Envelope plus fine structure alignment. 
+.RS
+Perform envelope-peak alignment as in option -1 and then shift the 
+fine structure phase in each channel so that a fine- structure peak 
+coincides with the envelope peak. 
+.RE
+.TP 7
+-4
+Envelope plus peak alignment, `left justified'. 
+.RS
+Align the envelopes and fine structure of all of the impulse responses 
+along the left edge of the image. 
+.RE
+.TP 6
+0
+No phase compensation. 
+.TP 7
++n
+Advance each channel by n cycles of the centre frequency of the channel. 
+Approximate envelope alignment is achieved using phase_gtf = 3 
+or 4.
+.RE
+.LP
+We experimented with a number of phase compensation schemes 
+(Patterson et al., 1989) and concluded that the best option was 
+envelope plus peak alignment which corresponds to a value of 
+phase_gtf = -4. Accordingly, we recommend the use of phase_gtf 
+values of 0 (ie no phase compensation) or -4 (envelope plus peak 
+alignment). The remaining options are occasionally useful and so 
+they have been left in the software.
+Note that for any phase compensation option other than 0 the time 
+scale is strictly correct only for the lowest channel. For any 
+other channel, the origin of the abscissa is offset to the right 
+by an amount equal to the difference between `the envelope peak 
+time of the lowest-frequency channel' and `the envelope peak time 
+of the given channel'.
+.RE
+.LP
+.SH REFERENCES
+.LP
+.RE
+.TP 4
+de Boer, E., and de Jongh, H.R. (1978). On cochlear encoding:
+potentialities and limitations of the reverse-correlation
+technique, J. Acoust. Soc. Am., 63, 115-135.
+.RE
+.LP
+.TP 4
+Carney, L.H. and Yin, C.T. (1988) 'Temporal coding of resonances
+by low-frequency auditory nerve fibers: Single fibre responses
+and a population model', J.Neurophysiology, 60, 1653-1677.
+.RE
+.LP
+.TP 4
+Cooke, M.P. (1993). Modelling Auditory Processing and
+Organisation, Cambridge University Press.
+.RE
+.LP
+.TP 4
+Giguere, C. and Woodland, P.C. (1994). A computational model of
+the auditory periphery for speech and hearing research. I. Ascending
+path. J.Acoust. Soc. Am. 95: 331-342.
+.RE
+.LP
+.TP 4
+Glasberg, B.R. and B.C.J. Moore (1990). Derivation of auditory
+filter shapes from notched-noise data. Hearing Research, 47,
+103-138.
+.RE
+.LP
+.TP 4
+Greenwood, D.D. (1961)  'Critical bandwidth and the frequency
+coordinates of the basilar membrane', J. Acoust. Soc. Am. 33,
[phone].
+.RE
+.LP
+.TP 4
+Greenwood, D.D. (1990). A cochlear frequency-position function
+for several species - 29 years later. J. Acoust. Soc. Am., 87,
[phone].
+.RE
+.LP
+.TP 4
+Holdsworth, J., Nimmo-Smith, I., Patterson, R.D. and Rice, P.
+(1988) Annex C of 'Spiral Vos Final Report, Part A: The
+Auditory Filterbank,' APU report  2341.
+.RE
+.LP
+.TP 4
+Johnstone, B.M. et al. (1986). Hear Res. 22: 147-153.
+.RE
+.LP
+.TP 4
+Moore, B.C.J and Glasberg, B.R. (1983), "Suggested formulae for
+calculating auditory filter bandwidths and excitiation patterns,"
+J. Acoust. Soc. Am. 74, pp 750-753.
+.RE
+.LP
+.TP 4
+Patuzzi, R., and Robertson, D. (1988) "Tuning in the mammalian
+cochlea," Physiological Reviews 68, 1009-1082.
+.RE
+.LP
+.TP 4
+Patterson, R.D. (1976). Auditory filter shapes derived with
+noise stimuli. J. Acoust. Soc. Am., 59, 640-654.
+.RE
+.LP
+.TP 4
+Patterson, R.D. (1987). A pulse ribbon model of monaural phase
+perception. J. Acoust. Soc. Am., 82, 1560-1586.
+.RE
+.LP
+.TP 4
+Patterson, R.D., Nimmo-Smith, I., Weber, D.L., and Milroy, R.
+(1982).  The deterioration of hearing with age:  Frequency
+selectivity, the critical ratio, the audiogram, and speech
+threshold.  J. Acoust. Soc. Am., 72, 1788-1803.
+.RE
+.LP
+.TP 4
+Patterson, R.D., Allerhand, M.H. and Holdsworth, J. (1992)
+'Auditory representations of speech sounds', In Visual
+representations of speech signals, Eds. Martin Cooke and Steve
+Beet, John Wiley & Sons. 307-314.
+.RE
+.LP
+.TP 4
+Patterson, R. D., Holdsworth, J., Nimmo-Smith, I., and Rice, P.
+(1988). SVOS Final Report: The Auditory Filterbank. APU report 2341.
+.RE
+.LP
+.TP 4
+Patterson, R.D. and B.C.J. Moore (1986). Auditory filters and
+excitation patterns as representations of frequency
+resolution. In: Frequency Selectivity in Hearing (B. C. J.
+Moore, ed.), pp. 123-177. Academic Press, London.
+.RE
+.LP
+.TP 4
+Schofield, D. (1985) 'Visualisations of speech based on a model
+of the peripheral auditory system', NPL Report DITC 62/85.
+.RE
+.LP
+.TP 4
+Slaney, M. (1993) An efficient implementation of the Patterson-
+Holdsworth auditory filter bank. Apple Computer Technical
+Report #35.
+.RE
+.LP
+.TP 4
+Zwicker, E. (1961) Subdivision of the audible frequency range into
+critical bands (frequenzgruppen).  J. Acoust. Soc. Am.  33, 248.
+.LP
+.SH EXAMPLES
+.LP
+The following command generates basilar membrane motion using the
+gammatone filter design (the default) for an input filename cegc:
+.RE
+.LP
+example% genbmm cegc
+.RE
+.LP
+The following command generates basilar membrane motion using the
+gammatone filter design (the default) for a filterbank with cf from
+200 Hz to 5000 Hz at a density of 4 filters/critical band for the same
+input filename:
+.RE
+.LP
+example% genbmm channels=0 mincf=200 maxcf=5000 dencf=4. cegc
+.RE
+.LP
+The following command generates basilar membrane motion using the
+gammatone filter design (the default) and the audiogram function
+instead of the outer/middle ear filter:
+.RE
+.LP
+example% genbmm middle_ear=off audiogram=on cegc
+.RE
+.LP
+The following command generates the basilar membrane motion using the
+transmission line filter design instead of the default gammatone
+filter:
+.RE
+.LP
+example% genbmm filter=tlf cegc
+.RE
+.LP
+The following command generates the basilar membrane motion using the
+transmission line filter design and the auditory scale of Greenwood
+(1990):
+.RE
+.LP
+example% genbmm filter=tlf bwmin=22.85 quality=7.238 mmerb=1.0 cegc
+.RE
+.LP
+The following command generates the basilar membrane motion using the
+transmission line filter design, but with the nonlinear outer hair
+cell feedback mechanism turned off:
+.RE
+.LP
+example% genbmm filter=tlf feedback=off cegc
+.LP
+.SH FILES
+.LP
+.TP 13
+ .genbmmrc 
+The options file for genbmm.
+.LP
+.SH SEE ALSO
+.LP
+genasa, gensgm
+.LP
+.SH BUGS
+.LP
+There is a bug in the hiddenline plotting of genbmm. It shows up when
+the surface has deep valleys and there is a large phase delay. The
+negative peaks show through on surfaces where they should be hidden.
+.SH COPYRIGHT
+.LP
+Copyright (c) Applied Psychology Unit, Medical Research Council, 1995
+.LP
+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.
+.LP
+The MRC makes no representations about the suitability of this 
+software for any purpose.  It is provided "as is" without express or 
+implied warranty.
+.LP
+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.
+.LP
+.SH ACKNOWLEDGEMENTS
+.LP
+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.
+.LP
+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.
+