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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A+B/A-B Components

What are the A+B components? The three primary elements in the recording, Lead Vocal, Bass and Kick Drum, are generally placed dead center in the mix (i.e. they have identical levels in both Left and Right channels). The academic power vocabulary way to describe stuff panned to the center is to say, “It’s in A+B, man.” When you listen in A-B, all A+B signals will be eliminated. When these are gone, you are left with both some pretty obvious stuff (everything that was on the left or right) and some less obvious stuff, like the reverb trails and delays of the lead vocal, effects, stereo filler, etc.) Some of this is pretty interesting. Numerous production effects and practices will be revealed, including various “tricks" with occasionally doubled words, rhythmic bounces between channels, special out-of-polarity effects and other elements of multi-track stereophony.



	The multitrack stereo field reconsidered. A and B can be thought of as special cases of A-B that come strictly from the Left and Right speakers. The stereo information and filler goes in the zones between Left & Center and Right & Center, as well as outside the speakers. A+B contains the core elements: lead parts, bass and kick.

Listening in A-B, you will hear a lot more of the stereo ingredients in a sound. A mono phantom image will be nulled out and a stereo phantom will have components remaining. Early delays added in mixing and panned left and right will be clearly revealed. Phasey stereo effects will show up as flanging. If they are keyed to the rhythm of the music, it will be obvious.

You also can have a lot of fun picking out things that the producers never intended you to hear: production flaws such as sloppy edits (often the A+B component masks the edit), poor azimuth alignment on analog recordings (high frequencies won’t be nulled and so you’ll hear wispy traces of A+B elements “leaking” into the A-B signal), artificial stereo reverb added to mono reissues (the mono will be gone, leaving you to listen to just the stereo reverb returns ), and so on. Old records can be a lot of fun in this regard.

See SIDE-BAR 2: A-B Unplugged - Classical Recordings

NEXT> Things you'll start to notice

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COMMENTS

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

A+B/A-B Components

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