Papers: Sonic Differences between identical CDsThe Numerically-Identical CD Mystery: A Study in Perception versus Measurement
The authors investigate claims that numerically-identical CDs can sound noticeably different on replay. It has been suggested that these differences are attributable to variables in certain processes in the CD production chain. The investigation centred on the controlled pressing of a set of test CDs encompassing the suspected variations. The discs contain test signals as well as music, so that listening test results can be compared with objective measurements from the same physical discs. This paper describes efforts in comparing listening test results with 'conventional' audio measurements.
The work described in this paper was begun early in 1996 as a result of reports, which abounded at that time, of different pressings of the same material exhibiting markedly different sound qualities on replay. An interim report on the progress the work was published in November 1996.
The usual scenario was that pre-mastering engineers or their clients would notice that a particular CD pressing would sound different from the original 'master tape' in the studio. Often, the same material would be re-pressed (perhaps in a different plant) and would sound better.
The affected discs reportedly had been verified to contain identical data to the master. However, it soon became clear that it was difficult to establish whether the comparison had been performed 'scientifically' in many cases.
There were a number of specific questions which needed to be answered in order to further our understanding of the problem, and this proved difficult - a lot of the evidence was more than second-hand, and many of the tales were probably apocryphal. It was therefore determined to go 'back to square one' - to take nothing on trust.
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