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Re: Get lost, Mr. Cochlea!! --- The Brain (Jont Allen )
Jont Allen wrote in
>The ear IS similar to a floating point converter. The ear does not have
>dynamic range or signal to noise ratio. This limited dynamic range
>shows up as masking. Do you disagree?
I don't know, but masking of a weak signal due to an intense signal in
its neighbourhood, is it entirely due to what happens in the periphery?
(We know about asymmetry, spreading and shifting of excitation to higher
What if the periphery still accurately (to the extent it is
allowable by timing jitter etc) represents the weak and intense signal
combo and the higher centers ignore the weak component, say, because
there is much more precise phase locking to the intense signal.
I am not too hot on the trail in masking.
Is it established that the information loss (masking) is entirely due to
Jont Allen wrote:
>The auditory nerve signal is not about zero crossing. Even zero
>are not exact, and would have jitter. But masking is NOT timing jitter.
We thought the classical theory of a neuron firing says that if the
membrane potential exceeds a threshold then it fires. If so, then it IS
some form of zero or level crossing detector. It is a question of how
the cochlear mechanics transforms the signal and presents it to the
Zero-crossings, as descriptors of a signal, have acquired
an undeserved bad reputation. As we have pointed out in our
original post, the zero-crossings of a STIMULUS SIGNAL,
themselves are NOT of much use.
But there are ways to carry reliably in zero-crossings (of other
information about the temporal envelope and phase of a stimulus signal,
thereby implicitly, but completely representing a signal.
This is our Main point.
Those familiar with speech signal processing know
about what is called Line-Spectrum-Frequencies (LSFs)
originally proposed by Fumitada Itakura, which represent
the spectral envelope of a signal. These LSFs are used reliably and
successfully in speech coding, recognition etc. These are
indeed 'zero-crossings' that represent the
spectral envelope, except that these zero-crossings occur along
the frequency axis, instead of time axis. Thus, there is already
albeit in the other (frequency) domain that these
the zero-crossings are reliable.
On a lighter note, I asked Yadong Wang (my grad student), two years
ago, to take a look at zero-crossings after reading your 1985 paper
in which you seemed to be saying that the auditory nerve signal IS based
on zero-crossings. (Jont B.Allen, "Cochlear Modeling", IEEE Acoustics,
Speech and Signal Processing Magazine,January 1985, p.3-28.) Refer to
and Figure 26 in this paper. Quoting from captions of Figure 25:
"Based on the model of the haircell, we assume here that the information
is carried by the zero-crossings of the multitudinous narrow band
signals. This is because the hair cell cilia appear to act as a switch,
given moderate and high level signals, transforming the signals
to peak-clipped signal. In an infinitely peak-clipped signal the
the information is coded by the zero-crossings..."
It is heart breaking to see that you would abandon zero-crossings and us
Subject: Re: Get lost, Mr. Cochlea!! --- The Brain
From: Jont Allen <jba@RESEARCH.ATT.COM>
Date: Tue, 27 Feb 2001 00:01:19 -0500
This is all very cute, and I dont want to be accused of not having a
sense of humor,
(clearly you do, and it is refreshing), but there is a thing called
Information is lost in the early auditory stages, due to neural coding.
The auditory nerve signal is not about zero crossing. Even zero
are not exact, and would have jitter. But masking is NOT timing jitter.
The ear IS similar to a floating point converter. The ear does not have
range or signal to noise ratio. This limited dynamic range shows up as
Do you disagree?