by humanracer » Wed Aug 01, 2012 8:35 am
"Some early digital recording & playback equipment, including CD players, used 14-bit converters, even though they were dealing with 16-bit audio. Some also used noisy "brick wall" filters to remove frequencies higher than the Nyquist frequency (22050 Hz). The resulting noise introduced by these converters and filters could be made relatively quiet by using pre-emphasis: boosting the signal (especially the higher frequencies) in the recording before it was put onto CD, and embedding flags in the disc's subcode to tell a CD player to apply de-emphasis on playback. Some CD players even had a de-emphasis button that could be used to manually apply de-emphasis, but now it's just a built-in feature of the analog outputs of nearly all dedicated audio CD players. By the late 1980s, pre-emphasis stopped being used because reliable 16-bit DACs with oversampling and other technologies minimized the conversion & filtering noise without the need for pre-processing the recording.
Most major-label CDs with pre-emphasis were manufactured in Japan in the early and mid-1980s. Relatively recent forum posts indicates that pre-emphasis is still used on newly manufactured CDs by some indie labels, mainly for classical titles. "