[Flac] understanding decorrelation

[Ulrik Nissen]

Hi FLACers

I'm studying music production and am currently doing an analysis of the FLAC format. If anyone has the knowledge and a minute to explain i would greatly appreciate any help. One thing that i cannot make sense from in the FLAC documentation (a thing that is hard to find info on in general) is how the decorrelation fase works exactly. I understand that the two channels in a stereo file can have similarities that can be exploitet when compressing, but why is this transformation used: mid = (left + right) / 2, side = left - right? Is it simply to straighten out the signals and thereby having less information to compress? 

I would really appreciate any help as there are many articles mentioning the transformations used by different formats in the decorrelation stage, but not exactly how it's a applied, but anyway - if you got this far - thanks for reading.

Rick
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