Re: Selective numbing ("Alain de Cheveigne'" )

Subject: Re: Selective numbing
From:    "Alain de Cheveigne'"  <alain(at)LINGUIST.JUSSIEU.FR>
Date:    Mon, 31 Aug 1998 13:16:13 +0200

>Although I don't have knowledge of formal studies on this (neither >articles) maybe I can add some more flavour to the discussion presenting >an effect I've been experiencing when exposed for some minutes to >"buzzing" noises due to poor shielded microphones cables (bad ground or >bad shield). > >After hearing this kind of noise for over 5 minutes (not loud, close in >intensity to a normal human conversation) and turned off the mic (so >stopping the noise) I noticed that all human voices I heard for some >time were kind of "flangered", even my voice sounded as if flanger >effect were being applied. It seems the noise had biased the hearing >hardware so that incoming voice were just analysed with a different bias >and producing a flanger effect. I didn't analyse the noise signal, but I >suspect it is probably very rich in 60Hz (the AC power supply >frequency). I'm not sure what is the processing within a "flanger". Is it a kind of time-domain comb filtering (ie subtraction or addition of the signal to itelf after a delay)? If so, it might be worth considering that the effect is be due to the lingering effects of a "harmonic cancellation filter", such as I proposed in some recent modeling papers (JASA 93, 3271-3290, JASA 101, 2857-2865, JASA 103, 1261-1271). The cancellation filter performs a kind of delay-and-subtract processing of neural spike trains within each channel coming from the auditory periphery. I speculated that the auditory system might try systematically to suppress parts of sound that have a regular steady-state structure, for example harmonic. Microphone hum is a good candidate, because it consists presumably mostly of 60 Hz-spaced harmonics distributed across the spectrum. This spacing is too narrow for peripheral selectivity to be much help in segregation, but time-domain filtering would be effective. Supposing that harmonic cancellation were "left on" after prolonged exposure to the hum, it might produce a "flanging" effect when the hum is turned off. Just a guess. Sorry for the advertising... Alain ------------------------------------------------------------------ Alain de Cheveigne' Laboratoire de Linguistique Formelle, CNRS / Universite' Paris 7, case 7003, 2 place Jussieu, 75251 Paris CEDEX 05, FRANCE. phone: +33 1 44273633, fax: +33 1 44277919 e-mail: alain(at) ------------------------------------------------------------------ Email to AUDITORY should now be sent to AUDITORY(at) LISTSERV commands should be sent to listserv(at) Information is available on the WEB at

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