Moulton Laboratories

the art and science of sound

Stereo Reconsidered: A+B/A-B: Another Way of Mixing

Dave Moulton, assisted by Alex Case and Peter Alhadeff

January 1993

1. The stereo image

2. Setting up an A-B signal

3. A+B/A-B Components

4. Things you'll start to notice

5. The "POL-REV" Button

6. A-B Unplugged: Classical Recordings

Comments (1)

Dave explains how to listen in A+B/A-B, or "Sum and Difference" Listening and Mixing.

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Sidebar 1: “IT’S NOT THE “PHASE” BUTTON, ITS THE “POL-REV” BUTTON.

Somewhere along the input section of most self-respecting console modules there is a little button, usually with the symbol “Ø” on it, that reverses the polarity of the voltages. Sometimes, the button will be called “Invert,” and once or twice I’ve seen the legend “180°.” Both “Ø” and “180°” refer to phase shift, and these references are misnomers, growing out of sloppy language usage by audio design engineers over the years. Phase shift relates to time delay or offset, and in fact there is no delay involved in the modest little circuit that the “Ø” button engages. Put simply, the circuit reverses the positive and negative voltages of the signal passing through. The reference to phase shift comes from the fact that if you look at an oscilloscope trace of a sine wave whose polarity has been reversed, it appears to have been offset in time by 180°. For years, design engineers have casually described it in such terms. A more accurate term is “pol-rev,” a contraction of “polarity reversal,” and I encourage its usage in better studios, bars and fast-food joints.

NEXT> A-B Unplugged: Classical Recordings

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Suriname Apr 19, 2007 08:59 AM

Hi David,

I purchsed your Playback series and I think it is worth every dollar invested.
I had some questions concerning the A+B/A-B technique.
I fully understood the defenition A+B and A-B, but what is not clear to me are the concepts.
On track 18 of cd#2 you centered the vocal, electric bass and kick drum and named it "A+B" and the rhytmic stuff was panned hard left and right and named "A-B".
What I have understood is that you have to mix the left channel (A) with the right channel (B) monaural into 1 channel (bounce) in order to achieve the "A+B" component.
To achieve the "A-B" component you have to mix the left channel "A" with the polarity inverted right channel monaural into one channel "A-B".
I than have 2 channels "A+B" and "A-B" and what is not clear to me is what to do now?
These questions I ask because I do only "voice over recordings" with high quality backing tracks that I record first on 2 channels of my Roland VS 880 VXpand digital workstation.
Given this configuration what is the procedure to apply the "A+B"/"A-B" technique?

Thank you in advance for your cooperation.

Ludwig Heidanus

Heidanus

Sidebar 1: “IT’S NOT THE “PHASE” BUTTON, ITS THE “POL-REV” BUTTON.

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