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[AUDITORY] Gammatone filter bank in MATLABr2019a



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
http://www.dtu.dk/english