EMUSIC-L Digest Volume 56, Issue 07 This issue's topics: Center channel extractor (3 messages) Your EMUSIC-L Digest moderator is Joe McMahon . You may subscribe to EMUSIC-L by sending mail to listserv@american.edu with the line "SUB EMUSIC-L your name" as the text. The EMUSIC-L archive is a service of SunSite (sunsite.unc.edu) at the University of North Carolina. ------------------------------------------------------------------------ Date: Mon, 13 Sep 1993 11:22:38 CDT From: Bob Crispen Subject: Center channel extractor I seem to recall that there's a way to hook up outputs (e.g., of a preamp or power amp) and use phase cancellation to produce a simulated rear speaker ambient sound. I also recall reading on EMUSIC-L a circuit diagram for Y-ing cables together which I saved and took home, since plain old Y cables are a Bad Idea. So these two thoughts rattling around in my otherwise empty brain produced a question: Is there an easy-to-build circuit that will take a stereo signal and produce: (a) the same signal less the center signals (i.e., stereo, but with a hole in the middle) and (b) the center signal only (i.e., a signal which is present in both L and R channels in equal amounts)? And (c) is it possible to control the width of the center hole? That is, if a signal is present in both L and R and the signal in L is at least n% (variable n) of the signal in R, it's extracted. Note that (c) isn't an absolute requirement if it makes the whole thing an order of magnitude more difficult. If a circuit that does something like (a) and (b), is easy to build, it might be fun to play with it and use it on a project only when it sounds OK. Or am I talking about something that the laws of physics won't let you do without a great deal of trouble (e.g., DSPs, microprocessors)? Thanks, +-------------------------------+--------------------------------------+ | Rev. Bob "Bob" Crispen | "IT FOUND ME!" | | crispen@foxy.boeing.com | Campus Crusade for Cthulhu | +-------------------------------+--------------------------------------+ ------------------------------ Date: Mon, 13 Sep 1993 17:08:36 -0700 From: Michael O'Hara Subject: Re: Center channel extractor It is easy to use op-amps to make a "center channel" filter. There is even a "nulling" ability. Invert one channel and feed it and the other channel into a "difference amp". This will give you R - L, or the "ambient" sound. You can expand the concept by adding/subtracting the difference signal from the left or the right channels, this is less useful. ------------------------------ Date: Mon, 13 Sep 1993 18:41:31 BST From: "Steven D. Bramson" Subject: Re: centre channel extractor Bob Crispen Writes --------------------------- Is there an easy-to-build circuit that will take a stereo signal and produce: (a) the same signal less the center signals (i.e., stereo, but with a hole in the middle) and (b) the center signal only (i.e., a signal which is present in both L and R channels in equal amounts)? And (c) is it possible to control the width of the center hole? That is, if a signal is present in both L and R and the signal in L is at least n% (variable n) of the signal in R, it's extracted. Note that (c) isn't an absolute requirement if it makes the whole thing an order of magnitude more difficult. If a circuit that does something like (a) and (b), is easy to build, it might be fun to play with it and use it on a project only when it sounds OK. ----------------------------------------------------- In the UK there is a science and technology TV magazine programme called Tomorow's World. A few years back they had what you might call an instant Karaoke machine. A black box electronic gizmo that looked for and removed part of the audio signal that is common to both left and right channels. You could pan this left and right, thus achieving (c) above. The application they suggested was that in a typical recording of a song, the instruments are left and right but the lead voice is in the middle. Using the gizmo you could knock out the lead singer and sing along yourself. I suspect the circuit was far from simple. Steven D Bramson Data Management Group JET Joint Undertaking Abingdon Oxfordshire OX14 3EA United Kingdom E-mail sdb@jet.uk Voice 0235 465 013 Fax 0235 465 399 ------------------------------------------------------------------ JET is Europe's fusion research project Disclaimer: Any views expressed are mine and do not represent those of JET ------------------------------ End of the EMUSIC-L Digest ******************************