Extracting lead guitar

These kinds of things have been posted several times before, but I’m not sure if I’m doing something wrong or if I’m trying to achieve something impossible.

I have a song with lead guitar, rhythm guitar, drums and vocals. I did the split-stereo-track-and-invert thing and now I have a nice track that has just about everything but the lead guitar and vocals.
Shouldn’t I now be able to invert the original song with this track, resulting with a track that only has the lead guitar and vocals? I actually tried it by using the original track and the result of the invertion and doing the split-and-invert thing again but I heard no difference though the other track’s visualisation (or whatever you call it) changed.

If this isn’t possible, spare me the jargon about sin waves and such :slight_smile:

You can isolate centre using spectral subtraction method, e.g. Kn0ck0ut plugin, (it does add digital artifacts).

But you can’t isolate centre using another inversion …

Re: seperate music from the singing ???
by stevethefiddle » Wed Nov 26, 2008 12:06 am

allencmcbride wrote:

But if you can remove the vocals, doesn’t that imply that you can isolate them as well? Once you have the two tracks, left and right, of just instruments, > couldn’t you invert them and add them to the original left and right tracks, leaving just the vocals? >


(quite tempted to leave it at that)
I wrote a full explanation somewhere on this forum, but a clue to why…

Left audio = L
Right audio = R
Centre audio = 2C

Left channel = L+C
Right channel = R+C

Remove centre audio: (L+C)-(R+C)=L-R (mono)

From the “left channel” and “right channel” (which you start with), there is no simple way to isolate C.
(spend 30 minutes driving yourself crazy with equations, squiggles on scraps of paper, and tests in Audacity, and you will come to the same conclusion, or start believing that you are Napoleon).

Instruments-in-the-middle cancellation is the only process that works out clean. You would think once you’re that far, you should be able to get the guitar back, but it doesn’t work like that.

The original guitar’s musical character came from the natural stereo show with all the blue waves right-side up. The new show is mono with half the blue waves upside down, so the new show is not simply the old show missing a few instruments.


Thanks for the answers!

Shouldn’t I now be able to invert the original song with this track, resulting with a track that only has the lead guitar and vocals?

Nope! :wink: I’ve been through this thought-process too and I know it seems like it should be easy, but no matter how much algebra you do, you end-up with essentially 4 possibilities:

Of course, there other math operations you can do like L-2R, etc., but there is no simple way to get the center (L+R) with the both the left & right subtracted-out.

**Now the good news…**There is a plug-in for Winamp called [u]DSP Centercut[/u] (FREE!!!), and [u]GoldWave[/u] ($50 USD) has an effect called “Stereo Center”. Both of these use DSP (digital signal processing) and can to extract the center channel. There are a couple of other similar effects if you search around.