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PostPosted: 22 Jan 2015, 14:52 
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Joined: 22 Jan 2015, 14:47
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Hallo there I'm hoping for some help with a schematic. It seems simple to remove center panned information with a few wires and switches like in vocal removers. http://makezine.com/projects/make-39/song-devocalizer/
What I would like is the opposite of that. To remove everything except centered panned information.

It feels like it should be easy to do electronically but searching for the answer is difficult!


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PostPosted: 22 Jan 2015, 22:42 
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Location: Arizona, USA
Hi, Yes what they did to remove the middle is easy. The opposite not so. A bit of background. The removal of the middle effect was used for a while in the 60s as a way to create two rear channels on systems that were initially only stereo. Several devices were marketed for it. I used to own one by Electrovoice. Essentially they used the out of phase components between the two channels to create a false set of rear ones. It created a nice effect. It was not however a true set of rear channels.

Now back to your request. To make it happen with a high degree of effectiveness will IMO require a bunch of circuitry. First it would need to identify the middle material. Then it would have to subtract it from the left and right channels. Finally it would then send the now subtracted signals to the outputs. It could be done with a number of IC OP amps used as buffers, inverters and comparators. Not a simple project but not too hard if you are good with ICs.

An somewhat less effective way can be accomplished with a few matching transformers. They will need to have outputs that are not shared with the inputs grounds. If you series them with the phases such that the + of one goes to the - of the other and take the remaining signal from the - of one and + of the other you will effectively add together portions of the signal that are in common and reduce effectively by half those that are not. The output will of course be monaural. This is a trick if you wish for improving the monaural output of a stereo phono cartridge when playing a monaural LP. It in that case not only doubles the output of the desired signal it will reduce the noise content because of the phase relationships.

Even though this is a diy site.....I believe I would personally seek some commercial gear to do what you want. Check out Pro audio sites for it. Some might be cheap.

Good listening
Bruce

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PostPosted: 22 Jan 2015, 23:56 
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Location: Chilliwack, BC
Matrixing is the term. For mathematical depth to Bruce's explanation:
https://en.wikipedia.org/wiki/Matrix_decoder

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* Ratings are for transistors - tubes have guidelines*
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PostPosted: 23 Jan 2015, 08:26 
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Hi, Gregg is correct, good link for those math oriented.

Good listening
Bruce

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PostPosted: 23 Jan 2015, 11:40 
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Joined: 22 Jan 2015, 14:47
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Oh that great thank you! Hmm considering it's getting technical (i.e things i don't understand) maybe I should ask the question directly then.

I'm trying to to get a left channel that consists only of left panned information.

My original thought was to use a center only channel for wave cancelling purposes.

Thank you so far!


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