Re: Rationale for Critical Bands

[James Johnston <James.Johnston@xxxxxxx>]

It's interesting. If you look at articulation index bandwidth, and presume, as seems to be the case but which remains enlightened speculation at this time, that it's the spectral peaks that define speech articulation, then 50 and 80 dB INTENSITY for speech would seem to be unsurprising.  

Consonance of chords arises from the harmonic beating, and there would seem to be no reason for the beating to change with level, regardless of the width of a cochlear filter.  This would seem to completely dismiss the relevance of cochlear filters totally, especially when accounting for things like co-articulation, etc, that do happen past the cochlea, that would capture beating even outside of an ERB to begin with.

Through all of this, I am somewhat bothered by the fact we keep seeing "dB, dB, dB", when we should be discussion phons or sones, unless somebody has refuted Zwislocki and Greenwood!

Is it the idea of the CNS proponent that "upward spread of masking" and the fact that excitation appears stronger at 2nd harmonic under high level conditions is due to the CNS???

While I've worked much more with phenomina than with the mechanisms themselves, the idea that response is faster at high frequencies and that masking is quite broader seems very consonant with wider ERB's/Barks, does a spectacular job of predicting the response of the codec listener, even with simplified stimuli, and introducing more mechanisms seems, frankly, to be asking for a visit from Ockham's Razor.

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-----Original Message-----
From: AUDITORY - Research in Auditory Perception [mailto:AUDITORY@xxxxxxxxxxxxxxx] On Behalf Of Martin Braun
Sent: Tuesday, June 15, 2010 6:10 AM
To: AUDITORY@xxxxxxxxxxxxxxx
Subject: Re: [AUDITORY] Rationale for Critical Bands

The best "experiments" for your answers are ordinary speech and music.

1) The quality of speech perception does not deteriorate when sound level 
increases from 50 to 80 dB.

2) The consonance vs. dissonance balance of a musical chord does not change 
when sound level increases from 50 to 80 dB.

These observations tell us that spectral filtering, including band 
filtering, in the auditory system is as good as unchanged in this level 
range.

We probably have lateral inhibition at all stages in the auditory pathway. 
This means that not only neural excitation is level dependent, but also 
lateral inhibition. Therefore it is no surprise that many experiments show 
level dependence in spectral filtering. Results vary with experimental 
design and say very little about real-life acoustical filtering such as in 
speech and music.

The central nucleus of the inferior colliculus (ICC) has a unique role in 
lateral inhibition, because here it is anatomically predetermined by the 
laminar structure of the nucleus. The mechanism of this nucleus enables the 
level independence of spectral filtering that we experience in speech and 
music.

The best descriptions of this mechanisms that I know of are in:

http://www.ncbi.nlm.nih.gov/pubmed/9237756

http://www.ncbi.nlm.nih.gov/pubmed/10190753

Martin


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