Ki-Young 2 mic sound field question (Jont Allen )

Subject: Ki-Young 2 mic sound field question
From:    Jont Allen  <jba(at)>
Date:    Sat, 19 Apr 2003 11:23:36 -0500

Dear Ki-Young It would be a good idea to add room reverberation of some form. The easy way to do this is to use the image method. For details see: (at)article{Allen79b, author = {Allen, J. B. and Berkley, D. A.}, title = {Image method for efficiently simulating small-room acoustics}, journal = JASA, volume = {65}, pages = {943-950}, year = {1979} } and the paper is posted at You will need djvu to view this, which may be downloaded from (or ). In the next week I will place some matlab code on my website that computes the room impulse response. In the mean-time, there is fortran code in the above paper. Another tweek is to add head defraction. There is code to do this as well, but I dont have the reference in my head. The work was done by Dick Duda. Do a search on google and you will find it. Jont Automatic digest processor wrote: > There is one message totalling 101 lines in this issue. > > Topics of the day: > > 1. Simulating a sound field and two mics > > ---------------------------------------------------------------------- > > Date: Thu, 17 Apr 2003 09:51:00 -0500 > From: Pradyumna S Upadrashta <prad(at)MAIL.AHC.UMN.EDU> > Subject: Simulating a sound field and two mics > > Dear Ki-Young, > > Simulating your situation is straightforward. It is essentially the > "forward problem" -- that is, you define a linear mixing matrix and > proceed to write out the linear model that describes the activity at > each microphone, given a specific source distribution. > > I'm more familiar with "forward" (you provide the geometry) and > "inverse" (no solutions without making assumptions) problems in EEG / > MEG analysis. > > Say Vout(i) is the voltage measured at your microphone, i, then you can > write the forward model as: > > Vout(i) = G1(i)*Y1 + G2(i)*Y2 + ... + Gn(i)*Yn + error > > Where G1, G2, G3,...,Gn are the individual "mixing matrices" for each > source Yk, with n sources total. > > Vout(1) is the output measured at mic 1 > Vout(2) is the output measured at mic 2 > > All you need now is a reasonable approximation of the geometry of your > scenario, which will determine the elements of the Gk's. It will have to > account for loss as a function of distance and medium. Presumably this > is constant for a given geometry, which is what allows us to write the > linear equation above; i.e., the loss w.r.t. distance is nonlinear since > sound amplitude should fall off as r^2; i.e., sound generically > propagates with a spherical wavefront and is described by > compression/rarefaction or longitudinal propagation. Of course the > situation is complex for different types of sound sources; for a good > overview, look at the following: > > > > > The Yk are the activity (amplitudes) of the sources over time, i.e., a > time-series of the amplitudes generated by the sources. > > The "error" term accounts for spurious background noises in the > environment (e.g., air flow around the mic head, spurious noises ala > 60Hz electrical frequencies, etc.). Measurement of the output of a > single/double microphone in a "silent" room might be a good > approximation of this term. > > Hope that helps. Or at least, hope it doesn't confuse ;-) > I might have missed something since I did this rather quickly. > > pradyumna > > __________________________________ > Pradyumna S. Upadrashta, PhD Student > prad(at) > 612-725-2000 x 1464 > > > > >>----- Original Message ----- >>From: "Ki-Young Park" <pkyoung(at)EEINFO.KAIST.AC.KR> >>To: <AUDITORY(at)LISTS.MCGILL.CA> >>Sent: 13 April 2003 17:23 >>Subject: correlation btw 2 singals incoming two ears from >>distributed souces >> >> >> >>>Dear all, >>> >>>I am working on the speech stuff, recognition and enhancement. While >>>using two signals with two microphones moderate distance >>> >>apart, say a >> >>>few tens of centimeters. I assume there is one speech source, >>>and distributed noise sources all around a room >>>instead of a point-source. >>>( and also assume additive noise. ) >>> >>>Is there publication on the correlation of two signals incoming into >>>two mics, when there are distributed noise sources around. >>> >>>and is there any way to simulate this situation? >>> >>>Any comments and references will be appreciated. >>> >>>Thank you. >>> >>> >>> >>------------------------------ >> >>End of AUDITORY Digest - 15 Apr 2003 to 16 Apr 2003 (#2003-84) >>************************************************************** >> >> > > ------------------------------ > > End of AUDITORY Digest - 16 Apr 2003 to 17 Apr 2003 (#2003-85) > ************************************************************** > > -- Jont Allen, 217/244-9567w; jontalle(at) Rm 4061, MC 251; Beckman Inst., 405 N. Mathews, Urbana, IL 61801; jba(at); JontAllen(at)

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Electrical Engineering Dept., Columbia University