Xref: utzoo rec.audio:8864 sci.electronics:4198
Path: utzoo!utgpu!attcan!uunet!seismo!sundc!pitstop!sun!decwrl!labrea!agate!pasteur!ames!ncar!noao!asuvax!anasaz!john
From: john@anasaz.UUCP (John Moore)
Newsgroups: rec.audio,sci.electronics
Subject: Re: Extracting Mono from Stereo
Summary: Here's how to do it (and how your ears do it)
Message-ID: <1436@anasaz.UUCP>
Date: 2 Nov 88 12:59:32 GMT
References: <343@ivucsb.UUCP> <3902@homxc.UUCP> <353@ivucsb.UUCP> <10744@cup.portal.com>
Reply-To: john@anasaz.UUCP (John Moore)
Organization: Anasazi Inc, Phoenix AZ
Lines: 48

In article <10744@cup.portal.com> R_Tim_Coslet@cup.portal.com writes:
]You wrote...
]>Might be doable in electronics, if variable time delays are available to
]>implement a correlator...adjust the delays for best mathcing in the two
]>channels, and knowing the delay, the heading is almost [sans ambiguity]
]>computalbe...with 3 ears, tis doable. With the digital sampling, and
]>digital correlators, should be doable...sample every 10 microseconds so
]>that even the high frequencies can be time aligned accurately.
]>
]>Any replies are appreciated.
]>
]>ALlen Sullivan
]
]Sure it is doable "with 3 ears"...
]However the original poster was asking how to do it with conventional
]2 channel "Left/Right" stereo. Which can't be done (as another poster
]has already said) because you can't generally solve 2 simultanious
]equations of 3 unknowns to unambigious results.
]
]I simply was explaining (to a poster asking "then how do the ears do it?")
]how they even frequently fail, except that your head can turn. The 
]"electronic head" in conventional stereo can't.

Using digital signal processing, implement the following:

(1) Spectrum analyze each channel into small bands
(2) On L, R, and Center speakers, implement a filter such that
the amount of any frequency band that gets through on L & R from
the original L & R sources is inversely proportional to how
balanced that frequency band is. Make the center directly
proportional to how balanced that frequency band is. Thus,
if a frequency band has equal amplitude on L & R, 0% of it
gets through to L & R speakers, while 100% gets through
on C. If a frequency band has 100% amplitude on L, and 0%
amplitude on R, then C=0%, L=100%, and R= anything you want
(x*0 == 0).

Basically, this approach treats a frequency band as a "sound" and
should be a fair approximation of how the ear works. To make
it better, use correlators rather than spectrum analyzers. To
make it simple, just break audio into 3 bands (with analog
filters) and go it all analog from there.

-- 
John Moore (NJ7E)           {decvax, ncar, ihnp4}!noao!nud!anasaz!john
(602) 861-7607 (day or eve) {gatech, ames, rutgers}!ncar!...
The opinions expressed here are obviously not mine, so they must be
someone else's. :-)