TheLastManWithBetamax:Super Audio Compact Disc An increasingly obsolete form of Super CD invented by SONY capable of playing 24 bit sound, and holding 5.1 mixes. There was a brief format battle with DVD-Audio, but here we are in 2009 and still listening to the original compact disc format, so both lost out and have vanished from the shelves to be the sort of thing you have to order. The PS3 can play the discs but you'll be hard pushed to buy one in your local Supermarket or HMV. Especially if your not a classical music fan. One frustration with the format i have found is attempting to get a player to send a signal via hdmi, coax or toslink, i gave up in favour of the analog jacks years ago.
Let's give a fairer appraisal for SACD...
Yes, increasingly obsolete unfortunately. Not through any fault of its own - it just so happened that it launched at the same tiem that people startign pirating music on the internet, and that method of acquiring music prevailed.
Most digital music and sound uses a method of encoding called PCM. Which due its mathematical nature is great for editing music. The downside is that PCM music can sound "clinical" to those who have experienced music in the real world, or on analogue media, e.g. vinyl. The big advantage of SACD on the other hand is that uses a technology called DSD. This is a digital encoding that follows the analogue soundwave very closely. It's a more literal digitisation of teh analogue waveform, but this points to anotehr reason for its demise - it was a new technology and was cumbersome to process in teh recording studio, and it meant that studios had to onvest in new technology...which didn't really pay for itself - once again, due to the prevalance of downloads.
Anotehr technical point is that SACD's liek DVD-A's were able to record and replay sound at above 20kHz (the upper frequency of human hearing). Sunds pointless, but there is scientific, and more importantly, anecdotal evidence from many reviewers, and listeners that this has a significant positive effect on treble in music.
Only the original PS3 60G can play SACD's - in the UK, no other models can. Although 99.9% of SACD's can play on any CD player.
There is no issue sending a SACD signal via HDMI as long as you stick to HDMI 1.2 or above. The onyl issue might be maintaining a DSD stream, as mentioned in my earlier post.