Pre-emphasis: All the 1983 Japanese copies of the Dark Side of the Moon CD have pre-emphasis.
What is pre-emphasis? - In the early years of CD manufacturing, a process called “pre-emphasis” was used to try and improve the sound of compact discs. Due to the fact that the analog to digital converters of the time period produced low level noise during the analog to digital conversion process, engineers used a method whereby high frequencies were boosted during the A/D conversion process, and the same frequencies were then reduced during D/A playback, thus eliminating the low level noise. In order for CD players to detect pre-emphasis on a CD, a “flag” was added to the digital data on the CD that the player detects, thus allowing it to “de-emphasize” the signal on playback.
