Xref: utzoo rec.audio:8745 sci.electronics:4157
Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!mailrus!cornell!uw-beaver!tektronix!tekgen!tekigm2!pavelz
From: pavelz@tekigm2.TEK.COM (Pavel R. Zivny)
Newsgroups: rec.audio,sci.electronics
Subject: Re: Extracting Mono from Stereo
Summary: how many knowns there really are ?
Message-ID: <3704@tekigm2.TEK.COM>
Date: 27 Oct 88 17:13:06 GMT
References: <343@ivucsb.UUCP> <3902@homxc.UUCP>
Reply-To: pavelz@tekigm2.TEK.COM (Pavel R. Zivny)
Organization: Tektronix, Inc., Beaverton,  OR.
Lines: 52

In article <3902@homxc.UUCP> marty@homxc.UUCP (M.B.BRILLIANT) writes:
:
:In article <343@ivucsb.UUCP> Todd Day explains his previous query:
: ....
:> Let's say the stuff in the left channel is L+0.5M (stuff that is not in
:> the center + half of the stuff that is in the center (mono)).  Right
:> channel is R+0.5M.  Now, I want just M....
:
:The man wants to solve two equations for 3 unknowns:
:	L + M/2 = known
:	R + M/2 = also_known
:L, R, and M unknown, solve for M.  Can't in general be done.

	 I guess I may have an idea, but I am not so sure if it's 
what you want; so let me ask you a question:

	What exactly is the M signal you are after ? Is it a signal similar 
to what would a mike with sphere characteristic placed on a vertical axis of
the scene pick ?  Or is it electrically added signal from R and L mike ?
(note-these two do differ a bit...) 	
	Or finally, is it more like what would a directional mike with a 
rather narrow characteristic laying on the axis of the sceen pick ? Not much
sounds from left nor right (music & effects), but everything from the middle
(the main dialog ) ?

	From the description of your problem, I assume it's actually the
last you are after. I believe you do have enough knowns for that last case,
at least under certain conditions; I'll elaborate on that if you confirm
that's what you want ....

(Tell us what exacatly do you want, and we'll tell you why we can't do it :-)

: ...
 deleted some stuff
: ...
:> you get R+L+M.  I want just M.  Subtracting the two channels gives you
:> R-L.  Subtracting the difference from the summation gives 2L+M.  I want
:> just M.
:> 
:> I need this to provide "centering" when listening to video tapes.  I want
:> to remove the mono from the stereo and put that through a speaker sitting
:> on the TV.  This way, no matter where you sit, you will always hear
:> conversation between on-screen people from the center.
:>  
:>    /| Todd Day (805)968-9352 |\            ....

	By the way, you can solve your problem by switching to silent
movies, too. :-)

|----- Pavel 
:-The opinions above are mine for the part found correct. Any errors )
 :- are due to malicious scrambling originated by Russian embassies.)