Re: [AUDITORY] Gammatone filter bank in MATLABr2019a

[Volker Hohmann <volker.hohmann@xxxxxxxxxxxxxxxx>]

Dear Dick and all,

just want to add that the re-synthesis method they apply is not optimal.
I would recommend using the Matlab implementations contributed by our
community, which have been described properly in citable publications,
are readily available and have been running flawlessly for many years
under whatever Matlab version came out.

Best regards,

Volker

On 17.04.2019 02:51, Richard F. Lyon wrote:
> Bastian,
> 
> That's an interesting distinction that needs to be made, between the
> peripheral and "whole system" auditory filter, whether gammatone or
> otherwise.  In my book, I say this about that (in Part III – The
> Auditory Periphery):
> 
>     13.1 What Is an Auditory Filter?
>     The auditory filters that we consider here include both those
>     motivated by psychoacoustic experiments, such as detection of tones
>     in noise maskers, and those motivated by reproducing the observed
>     mechanical response of the basilar membrane or neural response of
>     the auditory nerve. One thesis of this work is that a single model
>     can do a good job for both of these, and thereby provide a good
>     basis for a machine hearing system. Since there are several stages
>     of neural processing between the cochlea and our psychoacoustic
>     perceptions, it would not be surprising if the best parameters were
>     different between these types of models, but it seems likely that
>     the linear and nonlinear filtering due to the cochlea plays a
>     sufficient role in perception that we may find one set of parameters
>     is adequate, at least for a range of machine hearing applications.
> 
> 
> And to be fair, the gammatone was originally proposed as a model of frog
> hearing physiology, and is widely used in cochlear models, even though
> Patterson popularized it in the psychoacoustic domain.
> 
> So the MathWorks ought to be more careful what they say.  I'd have
> several other quibbles with their docs (in the Audio Toolbox reference
> at https://www.mathworks.com/help/pdf_doc/audio/index.html). 
> 
> Quibbles:
> 
> 1. "The gammatoneFilterBank follows the algorithm described in [1] and
> first proposed by [2]."  [1] is Slaney's method, a simple filter cascade
> based on analyzing the Laplace transform of the gammatone.  [2] is
> Patterson et al.'s "Complex Sounds and Auditory Images", a great paper
> but it doesn't say one word about how to implement the gammatone (they
> did have other implementation papers elsewhere, but not this method and
> not here).
> 
> 2. Ref 2 says "the shape of the magnitude characteristic of the
> gammatone filter is very similar to that of the roex(p) filter commonly
> used to represent the magnitude characteristic of the human auditory
> filter."  Mathworks says "The gammatone filter is similar to the roex
> filter derived from the notched-noise
> experiment."  A cursory look at more recent literature on auditory
> filters, including Patterson's, would suggest omitting or at least
> tempering this claim.  See my book Chapter 13 or this paper:
> https://storage.googleapis.com/pub-tools-public-publication-data/pdf/36895.pdf
> 
> 3. Error where it says b –– bandwidth, set to 1.019*erb2hz(fc).  Either
> the documentation is wrong, or the functionality is wrong.  Hopefully
> the former.
> 
> 4. The parameterization by only FrequencyRange, NumFilters, and
> SampleRate is rather impoverished.  It is not documented whether the
> filters match the ERB bandwidth if some of these parameters are changed,
> or whether adjacent filters continue to cross over about 3 dB down; you
> can't have both, but you might want one or the other, and there's not
> enough control to say what you want.  With a few more parameters one
> could do useful comparisons, tradeoffs, and tunings of filter numbers,
> orders, bandwidths, and phases for example.  With just a few more one
> could include better auditory filter variants (that differ only in the
> locations of the zeros of the cascaded second-order filters), including
> APGF and OZGF.
> 
> R2019a also adds gtcc (gammatone cepstral coefficients).  Their
> algorithm uses log(energy) before the DCT, instead of the cube root
> proposed by the Shao et al. reference, which also uses a slightly
> different acronym:  GFCC (gammatone frequency cepstral coefficients). 
> Not clear why.  The referenced paper did not really investigate whether
> their improvement over mfcc was due to the different frequency scale
> (700 Hz  mel vs 229 Hz ERB break point between linear and exponential
> spacing), or the filter shape (triangle vs gammatone), or the
> nonlinearity (log vs cube root), or the domain of implementation
> (frequency vs time). With the impoverished parameterizations of these
> functions in the audio toolboxes, it's hard to further compare such
> things (though the gtcc does allow some of that).  The other gtcc ref
> (Rabiner and Schafer) has nothing on gammatone or gtcc or gfcc.
> 
> I could go on...
> 
> Dick
> 
> 
> 
> 
> 
> 
> 
> 
> 
> On Tue, Apr 16, 2019 at 12:24 AM Bastian Epp
> <000000a94eb56441-dmarc-request@xxxxxxxxxxxxxxx
> <mailto:000000a94eb56441-dmarc-request@xxxxxxxxxxxxxxx>> wrote:
> 
>     Dear list,
> 
>     This morning I read through the release notes of MATLAB R2019a and was
>     happy to find that there was an implementation of a Gammatone filter
>     bank included:
> 
>     "Gammatone Filter Bank: Mimic the human auditory system"
> 
>     With the reference to (among others):
> 
>     Glasberg, Brian R., and Brian CJ Moore. "Derivation of Auditory Filter
>     Shapes from Notched-Noise Data." Hearing Research. Vol. 47. Issue 1-2,
>     1990, pp. 103 –138.
> 
>     This made me quite happy because it is a proper description of what
>     Gammatone filter banks most often are used for - to model the frequency
>     selectivity of the auditory system (as measured using psychoacoustics).
> 
>     However, in the DOC page, they show a picture of the Basilar membrane
>     on top with the frequency response of the filter bank - suggesting that
>     there exists a 1:1 correspondance.
> 
>     Everybody needs a topic to grow old and grumpy on - mine is this: 
> 
>     From my point of view, this is only correct under the (overly strong?)
>     assumption that the cochlear is the only place in the auditory system
>     underlying the perceptually observed frequency selectivity. Measuring
>     "auditory filters" means to evaluate the auditory system as a
>     whole (the concept of a "neuron" also only makes sense when being
>     embedded in its network). "Cochlear filters" are measured on/in the
>     cochlea . 
> 
>     Besides the common critiques (linearity, coarse approximation of the
>     actual "filter" shape, etc), the main problem in my point of view is
>     that we teach students that we can "measure" the function of a
>     "subsystem" (the cochlea) using a method that assesses the function of
>     the "whole" system. There are some data sets that suggest a strong
>     link, but the "tool" of psychoacoustics simply does not allow such a
>     statement.
> 
>     Even though I like the working hypothesis "The brain exists to keep the
>     cochlea warm", I think equating cochlear frequency selectivity with
>     auditory filters (without explicitly stating the assumption that no(!)
>     element along the auditory pathway modifies this frequency selectivity)
>     is a point where we could  be more careful to avoid misconceptions and
>     overly strong conclusions. In most publications and books, this point
>     is not explicitly wrong, but not as precise as it could be in my
>     opinion.
> 
>     I hope that someone from MATHWORKS follows this list and considers a
>     more careful description in the DOCs. I would also be happy to compile
>     all the constructive arguments that people might have for/against my
>     point of view.
> 
>     Have a great day everybody!
> 
>     BAstian
> 
> 
> 
> 
>     -- 
>     Bastian Epp
>     Associate Professor
> 
>     DTU Healthtech    
>     ------------------------------------
>     Technical University of Denmark
>     Ørsteds Plads
>     Building 352, Room 118
>     2800 Kgs. Lyngby
>     Direct +45 45253953
>     bepp@xxxxxx <mailto:bepp@xxxxxx>
>     http://www.dtu.dk/english
> 

-- 
---------------------------------------------------------
Prof. Dr. Volker Hohmann
Medizinische Physik and Cluster of Excellence Hearing4all
Universität Oldenburg
D-26111 Oldenburg
Germany

Tel. +49 441 798 5468
FAX  +49 441 798 3902
Email volker.hohmann@xxxxxxxxxxxxxxxx
http://www.uni-oldenburg.de/mediphysik/
http://www.uni-oldenburg.de/auditorische-signalverarbeitung/
Public Key and Key Fingerprint
http://medi.uni-oldenburg.de/members/vh/pubkey_vh_uni.txt
C75A 8A8D 9408 28EE FCFD 20CA 1D9F 23CC BAD2 B967
---------------------------------------------------------