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From: pvo3366@sapphire.OCE.ORST.EDU (Paul O'Neill)
Newsgroups: comp.dsp
Subject: Re: Psychoacoustics
Message-ID: <13729@orstcs.CS.ORST.EDU>
Date: 13 Nov 89 05:36:54 GMT
References: <1989Oct31.193130.1685@eddie.mit.edu> <1989Nov2.180644.28647@sj.ate.slb.com>
Sender: usenet@orstcs.CS.ORST.EDU
Reply-To: pvo3366@sapphire.OCE.ORST.EDU (Paul O'Neill)
Organization: Coastal Imaging Lab, Oregon State University, Corvallis, OR
Lines: 42

In article <1989Nov2.180644.28647@sj.ate.slb.com> greg@sj.ate.slb.com (Greg Wageman) writes:

>I don't think this is possible with two speakers in front of the
>person.  ..........

Wrongo.  See below.

>I'm by no means an expert, but my understanding is that the brain
>localizes sound by analyzing the amplitude (volume) and time-delay
>(phase) of direct and reflected sounds as percieved by both ears to ....

You've mentioned 2 mechanisms of localization, but not no. 3.

1]	Amplitude
2]	Phase
3]	Frequency response

Our ears have a different frequency response at different azimuths and 
elevations.  We use the frequency content of arriving sounds as one of
our localization inputs.

Demonstration:  Plug one ear with your hand.  Close your eyes.  Click
the fingernails of your thumb and forefinger on the other hand at 
various positions around your other ear.  Can you localize the clicks?
How?  You're only using one ear.

Ignoring 1] and 2], and building circuits exploiting 3] only can give
surprisingly good and adjustable stereo imaging -- with headphones or
with speakers.  One starts with the known frequency response curves of
the human ear for various azimuths the the known azimuth of the speakers
or headphones.  Filter the sound source such that when it is run through
the ear's "response at Speaker-Azimuth"  it will have the content of
"response at Faked-Azimuth".

I'll see if I can dig out my references on this stuff.  Most is from
Journal of the Acoustical Society of America. (JASA)


Paul O'Neill                 pvo@oce.orst.edu
Coastal Imaging Lab
OSU--Oceanography
Corvallis, OR  97331         503-754-3251