Xref: utzoo rec.audio:8669 sci.electronics:4117
Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!mailrus!ames!ucsd!ucsbcsl!comdesign!ivucsb!todd
From: todd@ivucsb.UUCP (Todd Day)
Newsgroups: rec.audio,sci.electronics
Subject: Extracting Mono from Stereo
Keywords: mono stereo signal processing
Message-ID: <341@ivucsb.UUCP>
Date: 20 Oct 88 22:57:34 GMT
Organization: The Audio Club at UCSB, Isla Vista, California
Lines: 35

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.

Your help would be greatly appreciated.  I'll summarize replies.


 
   /| Todd Day (805)968-9352 |\            "Hurt me, punish me.
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   \| Isla Vista, CA   93117 |/              todd@ivucsb.UUCP