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Re: surround sound tech info?

Hermann Stemberger replied to Jim Stevenson:
There are many types of Surround: Dolby Stereo (Analog, mono-surround
channel), Dolby Surround (Analog - also called "Pro Logic")

Just to clarify; Dolby Stereo and Dolby Surround are two different names
for the same encoding. Dolby Stereo was designed for the movie industry and
uses Dolby A or SR noise reduction, whereas Dolby Surround was targeted
to domestic applications and has no noise reduction (except internally).

switching between stereo on surround will always
be noticed because you're "switching on" (at least) one Surround-channel
(from the back!).

As a matter of fact switching _off_ the surround channels is more easily
detected, provided that the surround mix was properly done. "Switching on"
shouldn't be too detectable.

There are different socalled "upmix" (=make e.g. 5.1 channels out of 2)
algorhythms available. The most known is the (already mentioned) Dolby
Pro Logic Encoder.

Dolby Pro Logic only applies to _decoding_ a Dolby Stereo/Surround signal.
A Dolby Stereo/Surround encoder was designed to encode four channels
of audio into two channels. Yes, you can consider Dolby Stereo encoding as
an upmix algorhythm, but originally it is just an encoding algorhythm.

As far as i know there is just one professional headphone surround
system from STUDER that is in development stage.

That would be the BRS (Binaural Room Simulation) system, now developed
by IRT - Institut für Rundfunktechnik in Munich. More info at www.irt.de

The Dolby Headphone was originally developed by Lake DSP, and many of
the original forms of it and the hardware used is very professional.

The two mailing lists mentioned are probably the best sources for information
about surround sound. Here's one more discussion group, which deals a lot
with practical things:

Eero Aro
sound designer