07-09-12: Mrtennis
what about the obvious:
the master tape ages and when it is used to create a cd, the result is less than pleasant. this would be true for poorly maintained or old master tapes, maybe acetate-based.
Have you heard the remastered 45 RPM vinyl of Louis Armstrong, "Under The Stars," recorded in 1957?
There are more than a few new recordings that pale in the face of this early technology. "Satchmo Plays King Oliver," is stunning as well and equally old.
Your point is valid, some tapes have deteriorated but much was either bad to begin with or made worse by poor remastering.