Hi,
HDCD was originally developed by "Dr." Keith Johnson, a recording engineer, of Pacific Microsonics, and licensed out. It does not make a big audible difference. In fact, the technical explanation provided by Johnson at the time of its introduction was viewed as dubious by many in the A/V journalism community.
In fact, HDCD is a kind of compressor/expansion system that, with compatible players, will expand the dynamic range by about 6 dB to 10 dB. But, in some respects, it lessens the fidelity of a recording because if everyone isn't equipped with a decoder, then what they are hearing from a CD isn't as accurate as it might otherwise be with a non-HDCD-encoded disc.
Don't feel deprived if you don't have HDCD. DVD-Audio and SACD inherently deliver a far greater dynamic range than HDCD.
