From: schraudo%beowulf@ucsd.edu (Nici Schraudolph)
Subject: Re: Binaural stereo
Date: 17 Jun 90 06:30:58 GMT



aj14+@andrew.cmu.edu (Andrew David John) writes:
>If a computer could reproduce the echo/frequency-shifts/etc... that occur 
>when sound comes from a given direction and passes by the head, then it 
>could breate synthetic binaural stereo.

Computers are already used in the production of modern synth groups in
the way you describe, the main mechanism for creating an artificial
virtual location for a given sound (apart from the plain volume stereo)
being a phase delay between the two channels.  By varying that delay one
can achieve amazing effects of apparent motion of the sound source.

If you want to check this out I recommend listening to a couple of tracks
from the "League Unlimited Orchestra", if possible in the dark, with a
headset, and from CD for maximum impact.  The album has instrumental
versions of Human League's "Dare!" and actually overdoes this effect a
bit.  It is incidentally the album with the highest machinery/creativity
ratio I am aware of...

As for echoes, there was a computer system at the Linz Computer Music
Festival a couple of years ago that could reproduce virtually any echo
situation, in stereo.  It actually modelled whatever location you
wanted - ie. it did the audio equivalent of ray tracing.

>Does anyone know if the positioning mechanisms of the human auditory system 
>are understood?

Believe me, whatever people may tell you, *nothing* about the brain is
really understood - the best we have is educated guesses.  However, we
know from simple psychological experiments that the main factor for
locating sounds (for humans at least) is the phase delay I mentioned
above, with amplitude differences playing a secondary role.
--
--
Nici Schraudolph, C-014                nschraudolph@ucsd.edu
University of California, San Diego    nschraudolph@ucsd.bitnet
La Jolla, CA 92093                     ...!ucsd!nschraudolph