[wazoo2u]

Originally Posted by jcrab66

a true matrix is also the combined output of all single channel inputs into a soundboard through 2 channels

I've never heard the term applied to the configuration you describe. I would describe this (a regular soundboard recording) as a summed mix.

Actually, I would think that in concept, a matrix would exist within a soundboard as the relationship between all inputs and their ability to be selectively assigned to ALL outputs, at least, that's how I would commonly utilize any sort of routing or patching matrix, and that relationship is basically how a soundboard is defined ie: a rectangular array of elements (or entries) set out by rows and columns.

I believe that what we're discussing here is a recording technique that utilizes a specific kind of encoding, not routing. You can see the reference to MATRIX CO-EFFICIENTS in this description of MS technique: http://www.uneeda-audio.com/ms-mat.htm