Re: surround sound tech info?

[Eero Aro <arox@xxxxxxxxxxxxx>]

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:
http://www.musicplayer.com/ubb/ultimatebb.php?ubb=forum;f=16

Eero Aro
sound designer
arox@saunalahti.fi