Apologies to all for distributing this in error.  This is clearly off-topic
for a classical music list as these technologies are generic to all audio,
including music and movies.  I meant to respond to Walter privately, but I
sent it to the list instead, so I'll respond here.  Please don't submit a
response unless a clear, explicit connection is made to the classical music
listening experience.

Walter Meyer writes:

>Hoping not to have ventured out of the scope of what is appropriate for
>this list, what is "surround sound" 5.1 or otherwise? It sounds as though
>it's supposed to give you the illusion of having the music come at you
>from all directions.  But while that might be the way we would hear it as
>performers, it's hardly the way we'd hear it in a concert or recital hall.
>Maybe "5.1 surround sound" means something different.

Surround sound is not new.  Disney's "Fantasia" (1940) had discrete
6-channel sound, as did the Cinerama series of movies in the 50s.  Surround
sound in the home is not new either.  Fifteen years ago four-channel
surround was called "quadraphonic".  Indeed, the "Dolby Surround" (also
known as Dolby Pro Logic) system of today is not much different from the
CBS "SQ" matrix system of a decade ago.

Most of the "stereo" soundtracks used for laser video discs and VHS tapes
have been encoded for surround since the mid-70s, and even select classical
recordings have been made in using Dolby Pro Logic (usually demonstration
discs, cf.  Delos).

More recently, several discrete, or "5.1 channel" surround systems have
been introduced.  These use a compressed digital audio format, to provide
increased channel separation.  Two of competing schemes, AC-3 (aka Dolby
Stereo Digital - DSD - or simply Dolby Digital) and Digital Theater Sound
(DTS), were originally developed for theatrical use have invaded the home.
To use either system, a surround sound controller is required with the
appropriate decoding circuitry (some high-end AV receivers/controllers
support both formats).  In addition, six channels of amplification and
six speakers are required (left and right front stereo, a center channel,
a sub-woofer channel, and left and right rear channels).  With the right
electronics, and a well-engineered recording (all too rare) the effect in
classical music can be quite effective, putting the listener in a sweet
spot near the podium or in the first couple of rows of the auditorium.

The DTS "master-quality" mode for laserdiscs, compact discs, and DVDs,
uses less than one-fourth the data reduction of Dolby Digital, resulting
in what many consider audibly superior performance.  As with Dolby Digital,
DTS is an encode/decode system that delivers six channels (5.1) of
master-quality, 20-bit audio.  In the encoding process, the DTS algorithm
encrypts 6 channels of 20-bit digital audio information in the space
previously allotted for only 2 channels of 16-bit linear PCM.  Then during
playback, the DTS decoder reconstructs the original 6 channels of 20-bit
digital audio.  The claim is that each of these six channels is audibly
superior to the 16-bit linear PCM audio found on conventional compact
discs.  Dolby Digital uses a similar scheme, but with greater compression
of the surround channel audio signals, hence the lower perceived audio
quality sometimes mentioned.

For further information, check any of the numerous audio discussion lists,
and search the web.  There's a lot out there, including a lot of
misinformation.  I'd also recommend checking:

   http://www.dtsonline.com/
   http://www.dolby.com/ht/surr-age.html

and for a listing of the still-rare DTS-encoded classical releases see:

   http://www.image-entertainment.com/

Dave
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http://www.classical.net/