Xref: utzoo rec.audio:8908 sci.electronics:4209 Path: utzoo!attcan!uunet!husc6!bloom-beacon!oberon!skat.usc.edu!cuongla From: cuongla@skat.usc.edu (Cuong T. La) Newsgroups: rec.audio,sci.electronics Subject: Re: Extracting "Center Channel" from Stereo Image Summary: I think L X R is the solution... Keywords: stereo center channel mono Message-ID: <13278@oberon.USC.EDU> Date: 6 Nov 88 19:32:35 GMT References: <355@ivucsb.UUCP> <428@trwind.UUCP> Sender: news@oberon.USC.EDU Reply-To: cuongla@skat.usc.edu (Chris La) Organization: University of Southern California, Los Angeles, CA Lines: 40 Well I don't remember who originally asked for a simple way to extract the center channel from distince left and right channels but here is what I have came up with: Okay, lets forget about math for a while and concentrate on what we want. Suppose , we are watching Jonny Carson again and he is the only one talking at the moment. Instead of having half of his voice out the right channel and half out the left, we want him to sound out a third speaker at the center. At this instant, we probably want the side speakers to mute for clarity. However, anytime someone else who is not at the center speakes, we want the center speaker off and the side speakers back on. So , the following logic applies: let A equals L +.5M, B equals R + .5M, and X equal a control signal produced by A and B to control A and B. 0 is no signal, ED is ED Mc'man , Other is the other guy on the opposite side of ED, and Jon is of course Jonny we have: A B X -------------- 0 0 0 any EE majors out there will recognize the ED 0 0 table to be that of an AND gate. An AND 0 Other 0 gate can be represent mathematicly as Jon Jon Jon X = AB So, the answer is to take the channels and MULTIPLY them together. This creates a control signal suitable for turning the A + B (which is MONO) signal on or off at the appropriate time. Of course, we must have a circuit of sufficiently fast response so that only a very small time period is compared by the circuit at any given time. For something to start with, try digging up some basic digital circuit books and look up simple diode implimentation of the AND gate. Then replace the diodes with high value resistors. There you have it folks, either I am half right or half left... I mean half right or totally wrong about this so don't FLAME too much if it turns out to be another smart aleck answer... (ps, I hope this gets at least past the modem line I am calling on as this is my very 1st post on this system) Chris