Originally posted by newvox:
But it still plays with the laser refracted back rather than a clear reflection, hence the sound change even though it plays.
Well pardon me if I'm misunderstanding you (I only have an MSc in Music Technology, myself ;-) but you sound very much like you're under the misapprehension that there's a nice analogue relationship between the laser coming back and the sound output, like the way a needle reads a vinyl groove.
As you should be aware, CD's a binary digital medium
http://en.wikipedia.org/wiki/Compact_Disc#Data_structure The laser is either decoded as a 1 or a 0... provided there's no uncorrectable errors for a frame, it doesn't matter how dodgy the laser was, the PCM data is still reconstructed perfectly. If the media is so borderline that you're getting tons of uncorrectable errors (C2) then you'll start hearing skipping, glitching and the like - *not* a *subtle* "oh, this version of the CD sounds somehow better than the other one".
Anyway, pressing plants always QA checked things for those kind of errors.
I do recall doing an A/B test of the Virgin Metamatic CD with the Edsel one at the time, and seem to recall they did sound subtley different - this might suggest they were pressed from different digital transfers of the original analogue stereo master tape... certainly there'd been no drastic re-EQing or dynamics processing applied to them, which is probably a good thing!
The original vinyl Metamatic would of course have been mastered with an appropriate vinyl-EQ curve, to stop the needle jumping out of groove when the moog basses and CR78 bass drums kicked
As I'm sure many folk know, many CDs in the 80s were pressed from these vinyl cutting masters, with their attendant bass rolloff etc, and were digitized using wick A/D convertors,
and so sounded pants.
Conceivably, both the Virgin and Edsel CDs coulda been produced this way, but I doubt it...