l'HDCD pare abbia 4 bits in più del CD, che poi abbia un suono migliore è tutto da vedere.
Ecco cosa ho trovato Iè in inglese ma capibile) :
1. Standard CD (often called "Redbook") has 16-bits and 44.1 KHz worth of resolution. This was not arrived at back in the early 80's because it was "perfect" (marketing hyperbole aside), but because that was the maximum rez that cheap digital converters could be produced at with the technology of the day. It was a compromise.
2. HDCD is a sort of "hack" that tacks on a few extra bits worth onto a Redbook CD. HDCDs will play on any CD player, but you need an HDCD compatible player to "hear" those extra bits. There is much debate over the merits of this technology.
3. DVD-Audio is a new technology that has to have a DVD-Audio player to play back (at full resolution), you can't just use any old DVD player (although many DVD-Audio discs also have Dolby Digital versions of the music on them, but that is NOT full-resolution DVD-Audio sound) or CD player. DVD Audio has 24 bits and up to 192 Khz worth of resolution. Like the Redbook and HDCD, it is based on Pulse Code Modulation (PCM) digital technology. DVD-Audio discs used to be sold separately from CDs, but recently a new format called Dual Disc has allowed for the release of CDs with CD on one side and DVD Audio on the other. Many machines have a lot of trouble playing back either side of these discs, however. DVD-Audio can be in standard two-channel or in many cases, multi-channel surround if you have a surround system.
4. SACD is a totally different way of doing digital, not based on PCM. It has its supporters and detractors. Supporters claim it has vastly superior resolution to standard CDs. Detractors note that the DSD technology behind it is somewhat flawed, requiring serious noise-shaping in the high frequencies to prevent distortion. Supporters reply this has been addressed and very little music occurs up in the ultra high frequencies anyway (mostly out of the audible range), so it's a worth-while sacrifice for the extra resolution you get where it counts. Proof is in the pudding, and listening to SACDs reveals indeed they have superior sound quality to the CD, although they have a unique signature that doesn't sound very digital at all. SACD has a very analog signature which can be very appealing. DVD-Audio can sound like a CD on steroids, maybe a little more clinical than SACD. SACD also comes in several flavors and you need an SACD compatible machine to play it back. There are two-channel SACDs, SACDs with 2-channel and multi-channel mixes, and there are "hybrid" SACDs that will play on all CD players, but you can still only play back the SACD layer on SACD machines.
5. A Redbook CD played back on a high-quality CD system will sound better than a DVD-A/SACD played back on a mediocre or budget system.
6. Just because an album is encoded in HDCD, SACD or DVD-A is no guarantee it will sound great. It depends on how well the material was recorded, and how well it was mastered for digital. It's possible (and does occur) that some hi-rez titles do not sound better than certain other Redbook CD editions. But, when done right (and most of them are), hi-rez on a good system can be absolute *heaven*.