On 13 Dec 96  22:22:42 Chris Burgess typed to Bob Lawrence ....

Hi Chris

 >  CB>> No, that's not what I want. What I need is to pass the signal
 >  CB>> *identical* in both phase and amplitude on both inputs, and
 >  CB>> reject anything that's slightly different in either.


Maybe my brain is not grabbing hold of things properly, but what you
are  trying to do seems to be like my "fake" Quadraphonic system and the
idea may help.  I'm sorry but my brain can't pull it back to the opamp
level but here goes anyway...

 R ----------|............................
 pos         |                           |
             |                           |
             |   /|                      |   /|
          +  |-/  |                   +  |-/  |
 Normal Right  |  |                        |  |
          -  --\  |                   -  --\  |
             |   \|                      |   \|
             |                           |
 R-----------|                           |_______
 Neg                                            |
                                               \|/
 L ----------|                           /\/\/\/\/\/\
 neg         |                           |
             |                           |
             |   /|                      |   /|
          -  |-/  |                   -  |-/  |
 Normal Left   |  |                        |  |
          +  --\  |                   +  --\  |
             |   \|                      |   \|
             |                           |
 L-----------| ..........................|
 Pos

 The Above is a              The dotted section is added and only
normal Stereo wiring.        reproduces anything that is NOT in
                             both channels


No doubt you have seen the setup before, and with the speakers placed
suitably gives a good surround sound and adds movement to the music
depending on the original L R balance of the instruments.

To me, it does a good job of removing the "difference signal" out of the
main speakers and places it in the Aux speakers.

Whether the idea is usable in your application or not is not within my
current brain capabilities to calculate, but if it ain't then I have
just had some typing and ascii art practice. :-)


 >  CB>> The vocalist is dead centre, identical in phase and amplitude
 >  CB>> on both channels.

 And hence  will only appear in both Main LR channels

 CB> The pianist is 75% to the left.

 50% of which will appear in the AUX speakers, and 25% in each of the Main
Left & Right Speakers
 But as the right AUX speakers is wired in reverse to the Left main
 speaker this "audibly" reduces the sound location as the sound is 180
 degrees out of Phase.
 (how you apply this out of phase bit electronically is your baby:-))
 But even if you don't you have removed 50% of the Pianist from the Main
left channel speaker.


 CB>  The guitarist is 75% to the right.

 Same logic as above applies, but with L substituted for R and vicki
 verka.

You may now tell a brain damaged old pensioner to crawl back into his
shell.


CB> any ideas

You DID ask :-)

Cheers
Niels

* OLR 5.1 *  "A fool must now and then be right by chance." Ä
William Cowper

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