Masking ... was Re: Get lost, (flatmax )

Subject: Masking ... was Re: Get lost,
From:    flatmax  <flatmax(at)CSE.UNSW.EDU.AU>
Date:    Thu, 1 Mar 2001 04:33:34 +1100

As I understand it, the process of masking is the ability for a pitch to overcome the culminative pitch energies and stimulate the biological structures resident. If the culminative pitch energies are large enough, then they are liabel to supress higher auditory process stimulation by a lower energy pitch. Now my knowledge of the physical systems in operation is limited, however assuming the hair cells are inputs to neural networks, which fire most radicaly to frequencies with high power, and ignore lower power frequencies (during relaxation periods) then perhaps it is OK to argue that: Masking is the process of non-linear transmission from physical membrane movement energy to hair cell network energy. It can all be seen in the mathematical models of the physical entity ... i.e. the roll off in the tuning (masking) curves --- this roll off is not incredibly sharp on one side of the frequency of interest ... for this reason energy leakage or spreading may occur ... and for the same reason neural firing and relaxation periods (neural locking with or without phase) have the capacity to be swamped by other frequencies, other then the ones (at) the point of sensitivity..... So in my head I believe there is masking occuring as a process of transmission .... however I also believe masking may occur at more then one point in the auditory processing system, as suggested by your group (Ramdas) and the concept of "informational" masking brought up by David M. would apply for pitches which reside on the sharp roll off side of the cochlea. Matt On Mon, 26 Feb 2001, Ramdas Kumaresan wrote: > Dear Jont: > > Jont Allen wrote in > > > >The ear IS similar to a floating point converter. The ear does not have > > an infinite > >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 > > frequencies.) > 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 > > the > periphery? > > Jont Allen wrote: > >The auditory nerve signal is not about zero crossing. Even zero > crossing > >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 > neuron/haircell. > > 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 > related signals) > 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 > evidence > 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 > Figure 25 > 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 > > midstream. > > Rmadas Kumaresan > Yadong Wang > > xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx > > Subject: Re: Get lost, Mr. Cochlea!! --- The Brain > From: Jont Allen <jba(at)RESEARCH.ATT.COM> > Date: Tue, 27 Feb 2001 00:01:19 -0500 > > Yadong, > > 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 > masking. > Information is lost in the early auditory stages, due to neural coding. > The auditory nerve signal is not about zero crossing. Even zero > crossing > 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 > an infinite > dynamic > range or signal to noise ratio. This limited dynamic range shows up as > masking. > > Do you disagree? > > Jont >

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