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View Full Version : Removing 'common' Audio In A Stereo Domain



Jimbo
26th June 2005, 04:06 PM
Ok, so i'm having a crack at logic, express, and i was wondering if anyone could lend me their expereince in removing the centre channel, ie what is common to both left and right. I've tried inverting one channel and mixing it with the other, to no avail.

Basically i need to a) remove the vocal lines from a song wherein, the drums lie in the right, and the guitar in the left...

and then B) remove said drums and guitars leaving vocals...

I know i could do this in about 20 seconds using sound forge, man that s/w kicks ass... but i don't have a pc handy at the moment. and i can't find a good wave editor for mac. at all cheap or free or expensive!!!

-ta Jimbo.

marc
27th June 2005, 08:41 AM
There's a standard Logic plugin that'll do that and much more. Helper>DirectionMixer.

Base 2.0 = Complete centre removal.
Base 0 = Mono.

Good luck doing what you're attempting, it's almost impossible to isolate a part with modern recordings. I've had some success getting small bits out though, and you're going about it the right way.

Failing that, maybe try searching for an acapella.

Jimbo
27th June 2005, 10:47 AM
sorry, its logic express, i guess i'm missing the appropriate plugins...

i can't be assed now either... i'll just mess around with what i can get out cleanly...

Squozen
27th June 2005, 10:54 AM
http://audacity.sourceforge.net/

Works with VST plugins, so even if it won't do the trick natively you should be able to find something that will do the job.

marc
27th June 2005, 11:05 AM
You can easily do it by just using audio.

Basically, what you want to do to remove the centre is:
Mix the left channel with an inverted right channel and mix the right channel with an inverted left channel.

Just make a copy of the stereo audio file, then invert it. Once you've done that, set up the audio tracks in the arrange page like this:

Channel 1 :: A stereo channel with the original song.
Channel 2 :: A mono channel with the input selected as "Left" (hold down on the mono/stereo button for a second and a menu pops up... select "Left" from there). Use the inverted file on this channel.
Channel 3 :: Same as above, but for the right channel.

You can then use channel 2 and 3 to blend in the centre removal. If all channels are set to 0db, then it will be the same as the DirectionMixer with base set to 2.0.

oink
9th July 2005, 10:20 PM
Originally posted by Jimbo@Jun 26 2005, 04:06 PM
Basically i need to a) remove the vocal lines from a song wherein, the drums lie in the right, and the guitar in the left...

and then B) remove said drums and guitars leaving vocals...

I know i could do this in about 20 seconds using sound forge,
I doubt you could do it in Sound Forge.
'Reverse Karaoke' is virtually impossible.

The first process (karaoke) is not too difficult, but results can be less than stellar.

You need to separate Left and Right into mono channels, both panned center, phase invert one, then mix to a mono output.
It usually won't remove vocals completely, but reduce the center enough that oversinging will effectively obscure the original.

If you then use the same process to mix a mono version of the original with the version with center removed, but phase-inverted, you'll end up with something pretty similar to the original, because the left and right audio is also present in the center to a large degree.

BTW, AudioHijackPro has a vocal-removing feature.