[Pd] OT- FFT and human auditory cortex

Chuckk Hubbard badmuthahubbard at gmail.com
Thu May 25 01:09:57 CEST 2006

On 5/24/06, Charles Henry <czhenry at gmail.com> wrote:
> resonators at unstable equilibrium (like a hair trigger).  The cochlea
> encodes a train of phase locked pulses, which are transmitted by the
> auditory nerve, which contains both tonotopically and timing encoded
> (fine timing) information.  The cochlea can represent frequencies with
> timing encoding (I'm searching my brain for a better term than timing
> encoding, but not sure) up to around 5 kHz (it seemed a little high to
> me, when I first read the number...I thought it would be around 1
> kHz).

I mentioned this a little in my other response.  According to my
teacher, the nerves sending impulses arriving from the hair cells are
in bundles of 10, allowing higher frequencies to be perceived this
way.  But from about 100 Hz, the same frequencies are perceived
locally on the basilar membrane.  I guess.
By phase-locked pulses, do you mean that the hair-cell trigger happens
at the same point in each cycle, and so the resulting pulses correlate
to the same phase for each vibration?  If you mean something else,
it's probably not worth trying to explain.  But please do.

> (I can't remember these too well at the moment, I just graduated this
> spring...and my brains a little fried...there may be more.  I just
> feel like I've left some out)

"One had to cram all this stuff into one's mind for the examinations,
whether one liked it or not. This coercion had such a deterring effect
on me that, after I had passed the final examination, I found the
consideration of any scientific problems distasteful to me for an
entire year."
-Albert Einstein

> but the point (there IS a point) is that there are many different
> representations of frequency information along the auditory pathway.
> Each structure named does some kind of processing and passes the
> processing along to the next structure.  Ultimately, there are several
> different ways that sound is encoding up to and including the primary
> auditory cortex.  It is "like" and FFT, but it is also "like" a
> wavelet transform, and it is also "like" a bank of hair-trigger
> resonators.

But even if it's not FFT, doesn't it still make sense that you can
gather more information about a complex sound if you wait for a larger
chunk of it and average it all?  If nothing else, a shorter sound
would seem less likely to set all the relevant areas of the basilar
membrane in motion before it stops.  Supposedly one of the downfalls
of infrared MIDI guitar pickups is that there has to be a full cycle
of every frequency before it knows what notes to use, and the lowest
note on a guitar is around 82.5 Hz.
The popular Pd solution is overlapping windows, but I'm wondering if
there's something to running two simultaneous FFTs, with different
block sizes, gathering fine resolution in both domains.  I guess it
depends whether you're trying to reproduce the sound or just know what
it is.  For that matter, recording a sound at several different
sampling rates would give a finer time-domain picture.
There's probably someone somewhere who would know how to model a
cochlea in Pd.  I wish it was me.
If all of the resonators are moved by every motion, but a resonator's
motion only amplifies if it is repeatedly pushed in the direction it's
moving at any given part of its cycle, maybe it wouldn't be too hard.
Then again the energy absorbed by that resonator would be removed.
This is the sort of thing I would love to show my commercial-software
musician friends, a virtual cochlea modeled in free software.  Of
course few of them know what a cochlea is anyway.


> Chuck
> On 5/24/06, Chuckk Hubbard <badmuthahubbard at gmail.com> wrote:
> > http://cercor.oxfordjournals.org/cgi/content/full/11/10/946
> >
> > I came across this fact researching my final paper for Perception
> > class: the left auditory cortex is known to resolve temporal changes
> > in sound better, while the right auditory cortex resolves tonal and
> > harmonic information more finely.  As soon as I read this I thought of
> > FFT.  Could it be the difference between the brain hemispheres is
> > related to the auditory cortices having different block sizes?
> > -Chuckk
> >
> > --
> > "Far and away the best prize that life has to offer is the chance to
> > work hard at work worth doing."
> > -Theodore Roosevelt
> >
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"Far and away the best prize that life has to offer is the chance to
work hard at work worth doing."
-Theodore Roosevelt

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