🚀 go-pugleaf

in article 1130625124.508354.259710@g43g2000cwa.googlegroups.com,
maestro@ultrapiano.com at StpNrrs@aol.com wrote on 10/29/2005 18:32:

> Newsgroups:
> rec.music.makers.piano,rec.music.makers.synth,rec.music.compose,alt.music,alt.
> sci.physics.acoustics
> Subject: Re: how your ears work
> Date: 25 Oct 2005 18:38:23 -0700
> 
> p...@aol.com wrote:
> so what 'is' a sound?
> 
> maes...@ultrapiano.com wrote:
>> Inside the cochlea of a human ear are hundreds of thin cilia.  Rather
>> like an insect's eye, which is made up of hundreds of very primitive
>> eyes, each cilium responds individually to the pressure variations in
>> the cochlear fluid caused by sounds, contributing its own primitive
>> interpretation of the sound to the overall picture.  Each cilium
>> responds to pressure by firing a synapse and sending a bio-electrical
>> signal along the aural nerve into the inner brain, the journey taking
>> about a 25th of a second.  While a 25th of a second's worth of pressure
>> variation information is on the aural nerve's extensions into the brain,
>> the brain attempts to match its auditory memory with features in the
>> pressure variation information.  Neural pathways into the brain's
>> memory of pressure variation patterns are strengthened during this
>> process, resulting in the brain deciding on what the sound 'is'.
> 
> 
> From the brain's point of view a sound 'is' approaching from the left,
> for example, or a sound 'is' running water, or 'is' frightening, or
> pleasant.  The brain can detect such qualities without thought, because
> of automatic biologically evolved processes occuring within it, such as
> comparison of remembered pressure variation patterns with those in the
> sound.
> 
> Sound can be described mathematically as consisting of sinewaves at
> different frequencies and amplitudes, or as the numbers in a .wav or
> .mp3 file, but the information on the aural nerve is none of these.
> Each cilia fires when sufficient pressure above the ambient has been
> applied, and then takes about a 10th of a second to recover so that it
> is ready to fire again (by which time the internal pressure in the
> cochlea will usually have decreased to below the ambient for a short
> while).  Some cilia are less responsive than others and take more time
> to recover, but each cilium individually behaves like a very primitive
> ear, which becomes dormant for a short while whenever it has been
> squashed by the pressure in the ear sufficiently for its synapse to
> fire.
> 
> The hundreds of cilia individually send their primitive information
> along the aural nerve to the inner brain, and the brain can interpret
> the total of the sound information corresponding to a 25th of a second
> while it is on the aural nerve.  A loud sudden sound would probably
> cause a lot of cilia to fire simultaneously, along with low-level
> echoes, and the brain can detect that pattern of information as it
> travels along the nerve fibres.  High frequency sound might result in
> the frequent occurrence of large numbers of cilia firing in a short
> period of time, corresponding to a short length of the aural nerve on
> which the pattern is occurring.
> 
> The often-repeated belief (sometimes called the travelling wave theory)
> that the ear itself hears sound mechanically (rather than the brain
> doing the hearing and deciding on what a sound 'is'), with each cilium
> tuned by nature to respond to a specific sinewave frequency, and
> vibrating sympathetically to 'sound waves' of that frequency because of
> resonance effects in the cochlear fluid, and the basilar membrane
> detecting the strength of the vibration (rather like the base of a
> cat's whisker) to give the amplitude of a frequency, is basically quite
> ridiculous and should be abandoned.

i hadn't read through all this (and not guaranteeing that i will) but a
*very* interesting paper presented by a guy how designs signal processing
chips, some doing specific noise-shaping processing, was presented at IEEE
Mohonk 1997: http://www.icsi.berkeley.edu/~dpwe/waspaa97/program.html

it was Bob Adams (AD1890, ADI "sigma DSP", etc) "Spectral noise-shaping in
integrate-and-fire neural networks".  he also presented it the earlier EAS
convention in LA.  i saw both and thought it was a compelling theory.
anybody know an on-line source for the paper?

-- 

r b-j                  rbj@audioimagination.com

"Imagination is more important than knowledge."