The real improvement is with SACD (high resolution 24/96, multichanel, DSD) a real improvement versus standard CD in audio quality terms. HDCD is only a method for encoding 20 bit into a Red Book CD (16 bit 44Khz). They use specific hard and soft to do that. In fact it is a very interesting thing because they (now Microsoft but before an independent company,called Pacific Microsonics, who created the HDCD definition) convert the 16 bit to 20 bit but still record the information into 16 bit 44Khz CDs. So, It is a little bit confusing, because the question is, how can i listen to the 20 bit info if they still use a normal CD with 16 bit resolutioin? They answer that the additional 4 bit are encoded inside the CD using its HDCD technology. In fact to decode HDCD you need a CD with a PM-100 or PM-200 chip (or the algorithm impplemented inside a multidecoding chip). HDCD discs only use the 4 additional bits if a HDCD chip is present in the CD. If not, they play as normal CDs. The HDCD vs SACD is not the real point in the high-end audio world. The real point rigth now is DVD-Audio or SACD (MP3 and similars apart). In audio quality terms, and after listening carefully to both systems, SACD is better than DVD-Audio. It seems that DVD-Audio has loose the race due to protection copy techniques used on it becasuse they can be heard when listening carefully, as a noise.
