Totally unrelated to the usual topics, but still interesting (IMO): I have been really into multi-channel high-definition music for some time now and really enjoy SACDs and DVD-Audio discs. Chances are that you haven't eve heard about these formats yet, since the content mafia music industry decided to introduce these very exciting formats with no marketing at all. Both have been around in force since about 2001 and they deliver (sometimes) excellent 5.1 surround music in extremely high definition: 

• DVD-Audio (PCM)
  
• Stereo: up to 192 kHz/24 bit = about 4.3 times the frequency resolution of the Audio CD and 144 dB theoretical sound to noise vs. 96 dB with the Redbook CD (that's 256 time better).
  
• Surround (5.1 discrete channels): up to 96 kHz/24 bit - still more than double the frequency resolution than Redbook Audio CDs and 28000 Hz above the best human perception.
  
• These high-resolution formats are contained in the DVD-Audio section of the disc that CANNOT be read by a "normal" DVD-Player. You will need a special DVD-Audio or Universal player for this.
  
• DVD-Audio discs most often also have a DVD-Video section that typically contains the stereo track in standard 48 kHz/16 bit PCM stereo and sometime a DTS or Dolby Digital version of the surround mix. This section is playable in any standard DVD player.
  
• DualDisc DVD-Audios have two sides - one containing the DVD-Audio side, the other containing a CD Audio side.
  
• SACD (DSD)
  
• Instead of the usual PCM encoding, the SACD uses DSD encoding which is significantly different from PCM by using a single bit quantization at a relatively high sampling rate (2.8 MHz - yes, MEGA Hertz). The claim of the DSD fans is that the demodulated signal is closer to an analog signal when compared to PCM encoding. Opponents complain about the more limited S/N ratio at high frequencies, artifacts of the (necessary) noise shaping and - in general - about a too low sampling rate in the SACD specification.
  
• SACDs must have a stereo DSD track and most often also have a 5.1 surround DSD track. These tracks can only be read by SACD players (or universal players). Most times, the signal is only available as an analog signal, although there are some players (Denon 3910, Oppo, PS3) that convert the DSD signal into high resolution PCM and send it over HDMI to the DAC or receiver.
  

While DVD-Audio is most common in popular music (e.g. Talking Heads re-release on DualDisc), SACD is most common with Classic titles. Since the have had such a slow start from 2001 through 2006, many early adopting labels have either stopped DVD-A and SACD production completely right now, or are only releasing obscure titles or only a very limited selection. Notable exceptions to this are (in the Classical world): Tacet, MDG (DVD-Audio); Pentatone, Channel Classics, BIS, Alia Vox (SACD). Please check my del.icio.us links for online retailers.

Going forward, I expect that SACD will get a lot of attention, especially from the labels (see e.g. the Genesis re-releases on SACD). The reason for this is quite simple IMO: SACD the the *ONLY* format that has not been hacked so far - all others (including BluRay and HD-DVD) are copyable. And I think that this will stay like this for quite a while for the following reasons:

• There is no SACD drive for computers - that makes hacking infinitively more difficult.
• The copy protection mechanisms are not very well understood.
• There is no known way to create a SACD at home that can be played on a stock SACD player.
• Even if the SACD was hacked, there is virtually no mainstream hardware and almost no software support for DSD, making the digital data very mainstream unfriendly.

You might argue that you could sample the analog out at 96 kHz or better or capture the converted PCM from some hacked HDMI conversion player. All this would require a lot of expertise and probably some fairly expensive hardware, again making this approach not attractive to the mainstream user.

No even if you overcame all these hurdles, you'd need to play the 5.1 96KHz track somewhere. The only easy-to-use solution today is the creation of a DVD-Audio disc (which is not trivial or expensive). Alternatively, you would need a decent PC with a 6 analog out and some knowledge to configure the soundcard(s) properly ... not mainstream user, again.

Instead, they would simply copy the RedBook data from Hybrid discs and be happy. Therefore, I think that at least the SACD will survive the HD wars.

tag: DVD-Audio, SACD, High-Definition, Audio