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

```Subject: Ki-Young 2 mic sound field question
From:    Jont Allen  <jba(at)auditorymodels.org>
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
http://auditorymodels.org/jba/PAPERS/Allen/Allen79b.djvu
You will need djvu to view this, which may be downloaded from

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
> 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.
>
>
> __________________________________
> 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
>>>( 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)uiuc.edu
Rm 4061, MC 251; Beckman Inst., 405 N. Mathews, Urbana, IL 61801
http://auditorymodels.org/jba; jba(at)auditorymodels.org; JontAllen(at)ieee.org
```

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