From isc-newsserver!psinntp!psinntp!psinntp!sunsrvr6!slaw Wed Aug 24 20:17:00 EDT 1994
Article: 8358 of comp.sys.amiga.audio
Newsgroups: comp.sys.amiga.audio
Path: isc-newsserver!psinntp!psinntp!psinntp!sunsrvr6!slaw
From: slaw@cci.com (Scott Lawrence)
Subject: Re: SURROUND SOUND POSSIBLE???
Message-ID: <CusEsB.It6@sunsrvr6.cci.com>
Sender: root@sunsrvr6.cci.com (Operator)
Organization: Northern Telecom, Network Application Systems
References: <32ah3f$dhk@louie.udel.edu> <CuJCp9.Jqq@sunsrvr6.cci.com> <32o0ss$t79@quartz.ucs.ualberta.ca>
Date: Fri, 19 Aug 1994 14:55:22 GMT
Lines: 94

In article <32o0ss$t79@quartz.ucs.ualberta.ca>,
Hardin Brett Arvid <hardin@ee.ualberta.ca> wrote:
>Scott Lawrence (slaw@cci.com) wrote:
>| In article <32ah3f$dhk@louie.udel.edu>,
>| Steven Koukoulas <koukoula@latcs1.lat.oz.au> wrote:
>| >ok ok ok,
>| >	Anybody know how to get surround sound going through the amiga
>| >channels. is there any way to alter the sound frequencies to conform
>| >with what is necessary for SS.
>
>| We've _been_ talking about that for a while now.  read back a bunch of 
>| articles.
>
>| >P.S. Anyone want a challenge.
>| >     How 'bout writing a sound filter to convert a sound file making it
>| >     SS ready.
>
>| already being worked on...
>
>
>Suround sound is (in principle) easy.
>The front chanel would require you to put the EXACT same signal on both chanels.
>The rear chanel would require that the LEFT chanel be the INVERSE of the RIGHT.
> (This involves using two chanels for one sound though)

not exactly.  THere has to be an inverse between left and right to get the 
surround channel, (180 degree phase shift), but if this is done, and you
have the stright signal going through the left and inverted going through the
right, for the suround channel, lemme just say something... don't plan
on having what's in the surround channel being the same as the right channel.
that would cancel it out completely.  there would be no sound from the 
right channel.

ie:

to get:  (time is the horizontal)
(where it is the same sound in all channels. let's say a 60hz tone.  :)
(these are the result signals)
        __
L  ____|  |_____________________________
             __            __
R  _________|  |__________|  |__________
                  __
C  ______________|  |___________________
                        _________
S  ____________________|         |______



You're saying to do this:
(these are the encoded signals)
        __        __    _________
L  ____|  |______|  |__|         |______
             __   __    _________ 
R  _________|  |_|  |__|##%%%####|______

# indicates the inverted signal
% indicates where the right signal, and the inverted will cancel eachother

so these will be the resultant signals:
        __
L  ____|  |_____________________________
             __               
R  _________|  |________________________
                  __
C  ______________|  |___________________
                        __    ___
S  ____________________|  ----   |______


or something similar.

if you have a real 90' phase shift between the surround signals ansd
the left and right signals, you will not have to worry about this.  Being 
that we're also working with pure digital signals and timing here, it makes
these things more tricky.  If these were to be done with audio tape, and
analog equipment, you may not ever run into this problem, as the surround 
signal can be slightly echoed before it's inverted and sent to the surround
encoding (using your method).

Any way you look at it, you're going to get some sort of signal loss.

	-Jerr

any mail replies to jerry@mail.csh.rit.edu   this account (slaw) disolves
today.  :(


	
-- 
      Scott "Jerry" Lawrence           __  "I'm tired of this war
      jerry@mail.csh.rit.edu          ///      Go ahead and cut me
  http://www.csh.rit.edu/~jerry/  __ ///         I can't feel it anymore." - NIN
     #include "disclaimer.h"      \\X//   BleuLlama on IRC! #anime! #Amiga #NiN