Xref: utzoo rec.audio:8693 sci.electronics:4134 Path: utzoo!utgpu!attcan!uunet!lll-winken!lll-tis!helios.ee.lbl.gov!nosc!ucsd!ucsbcsl!comdesign!ivucsb!todd From: todd@ivucsb.UUCP (Todd Day) Newsgroups: rec.audio,sci.electronics Subject: Re: Extracting Mono from Stereo Keywords: mono stereo signal processing Message-ID: <343@ivucsb.UUCP> Date: 21 Oct 88 14:54:27 GMT References: <341@ivucsb.UUCP> Reply-To: todd@ivucsb.UUCP (Todd Day ) Organization: The Audio Club at UCSB, Isla Vista, California Lines: 59 In article <341@ivucsb.UUCP> I (Todd Day) write: _I have a very interesting signal processing problem for those signal _processing gurus. _ _I want to use a DSP chip to extract mono from stereo. Does anybody _know of any algorithms to accomplish this or can anyone direct me to _any literature that might describe this? _ _I've looked into the math behind this. It is not a simple as it first _appears! Now, it's very, very easy to get rid of mono from stereo... _just subtract left from right, and the mono disappears. However, you _can't just subtract this (R-L) from (R+L) to get only mono. What _you always end up with is some combination of the mono plus one of _the other channels (2M - 2R, etc.) _ _I've even thought about using "correlation math", but this only tells _me HOW MUCH mono is there, instead of telling me what the actual _mono is. _ _The only solution that I can think of is to mimic the human ear. _That is, break up the frequency spectrum into sections, and compare _relative levels of the frequencies. When they are approximately _the same, call that mono, and send the signal in that band through. _This would be computationally expensive, though, and I'd rather _not do it because it would not be entirely accurate. I am not _concerned about the way the ear checks phase differences for _directionality... I am assuming that the mono will be in phase. OK, guys, how about reading past the second paragraph? Since I only just posted this yesterday and got a couple of smart-aleck responses already, maybe I should clarify... I guess I confused everyone out there when I said "mono". What I mean by mono is not the same as the mono switch on an FM radio. What I am after is just the stuff in stereo that you hear in the center of the speakers. In other words, that means in that most of today's music, I am trying to extract only the singer's voice (and anything else that might be in the center). This is NOT R+L!!!! 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. If you add both channels together, 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. _Your help would be greatly appreciated. I'll summarize replies. Your smart-aleck answers are not appreciated. I won't summarize these. :-) /| Todd Day (805)968-9352 |\ "Hurt me, punish me. +-+ | The Audio Club at UCSB | +-+ Make me listen to mid-fi!" +-+ | 926 B Camino Del Sur | +-+ {}!pyramid!comdesign!ivucsb!todd \| Isla Vista, CA 93117 |/ todd@ivucsb.UUCP