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Surround sound - explanatory notes
General information:
The following section is not concerned directly with the
operation of your digital surround decoder, but is rather
intended to explain some of the terms which arise in
connection with surround systems. It is intended to help
you understand and exploit the facilities and capabilities
of your decoder to the full.
As we all know, a normal stereo recording has two chan-
nels - left and right. When stereo material is reproduced
in your listening room, the entire sound event takes place
on an imaginary stage which covers the space between
the two loudspeakers. The listener is able to locate spe-
cific sound events over the width of the stage; with good
recordings there is also a slight impression of depth, i.e.
behind the speakers. Nevertheless, normal stereophonic
reproduction always leaves the listener isolated from the
event.
As a result it is impossible to recreate the excitement of a
live atmosphere, as in a real concert hall, since the
acoustics of the concert hall are crucially influenced by
sound reflections from the side and back walls, the floor,
the ceiling, and from objects inside the building. The
reflected sound comes from any number of directions -
not just from the front.
If a sound event is to be reproduced with real fidelity, it
therefore follows that a proportion of the sound must
emanate from all directions in the room, that the “reflec-
tions” must be timed accurately, and that they must be
generated at a realistic level.
Reproducing television sound via a conventional stereo
system is problematic, because it is often impossible to
locate dialogue on the screen itself.
A further point is that exotic sound effects have been in
use in the cinema since the 1950’s, using proper multi-
channel sound systems. These effects are often crucial
to the overall impact of a film, but they cannot be repro-
duced at home with a conventional stereo sound system.
Over the last few years surround technologies have been
developed which make it possible to experience all these
effects within the listener’s own four walls, with the result
that a far greater simulation of reality is possible than
with conventional stereo.
For an effective surround system we always recommend
the installation of a center loudspeaker, which is installed
below or directly above the TV set. This loudspeaker
helps greatly in locating particular sound events (espe-
cially dialogue) on the TV screen itself.
Dolby Pro Logic II Surround
In this process serveral independent signal channels
(left, center, right, surround (rear) left and surround (rear)
right) are recorded using two channels and a special
encoding process. Since this process only requires two
recording channels, it is compatible with many picture /
sound systems which are already widely in use (CD,
video recorder, TV etc.).
The information is decoded at playback time and repro-
duced in the listening room via four (left, right, 2 x rear)
loudspeakers, although five speakers (with an additional
front center speaker) are preferable. Dolby Surround
encoded material is currently available mainly in the film
and video arena, recorded on video cassettes and DVDs,
but a large number of television programmes are now
being produced and transmitted using Dolby Surround.
