The M/S approach essentially considers it as being comprised of central and side elements. The Mid signal is the mono sum of both left and right, and basically describes those elements present in both channels. The Side signal is the difference between the two channels, and describes those elements that contribute to the stereo width… It follows from this that the balance between the Mid and Side signals determines stereo width.

Essentially the idea was to get out of a single signal both the in-phase information and the out-of-phase information… I began to try to figure out a way of tricking the signal so that part of it would play and another part might be cancelled. I then tried layering different frequency paths. Let’s say I took a limited frequency band up to, say, 3kHz. I’d let that play. Then I would take another band-limited signal from 3kHz to 6kHz and put it in the opposite phase. Now they’re playing together. They’re not interfering because the two are not really playing the same frequency simultaneously, If you keep doing that with other frequency bands, it’s like weaving frequencies. A group of frequencies will be in-phase to a limited bandwidth; another group of a different bandwidth will be out-of-phase; and I would add these layers until the entire audio bandwidth from 20Hz to 20kHz was covered. That technique produces a whole audio signal… We call it in our patent “Phase Layering.”