here is quote from the author of the program:

QUOTE:

Hello all, I've seen comments from a few people wanting to know how hdcd works, so I decided to take a look at it as an academic exercise. Attached is a 'reference decoder', which reads a 16-bit wav from from stdin, upconverts it to 24-bit using embedded hdcd information where present, and writes the output to stdout. To use, simply run: hdcd.exe < 16bit.wav > 24bit.wav If embedded hdcd information is detected, a notification will be written to stderr. Non hdcd's will also work, although the only result will be to halve their volume. Let me know how you get on, Chris it can be downloaded from: http://www.srcf.ucam.org/~cjk32/hdcd/hdcd.zip

so now we can enjoy HDCD at their full quality, as far as the HDCD information is still in the HDCD rips that can be found here, but let test and discuss ...