Lexicon DC-1 Supplementary Manual page 23

DC-1 Theory
and Design
20
sense of the music coming from all around you, but the violins and cellos are
equally loud from both sides.
Music Surround solves this problem in a novel way. The side speakers
reproduce the left and right front loudspeaker signals with two additions:
delay and inverse steering.
The delay serves a simple purpose. Sounds are kept from being localized to
the sides by an approximately 10ms delay inserted between the front and
side speakers. The center speaker is steered, and can be delayed relative to
the fronts. The center delay allows the center speaker to appear to be at
exactly the same distance from the listener as the front speakers, even if it
is placed (as usual) on a line between the front speakers.
Inverse steering acts to remove a strongly steered signal from certain
directions. As an example, assume you have a strong signal in the left
channel of a film. With normal steering, the processor enhances the level of
that signal in the left speaker, and actively removes it from the other
speakers. Inverse steering actively removes this signal from the left side
speaker, while keeping its level strong in the left front speaker. This signal
removal is done cleverly, so the level of any unsteered signal which might
be present at the same time (such as music in a film, or the rest of the
orchestra in a music recording) is not significantly reduced. The sonic result
is a much wider soundstage and a very spacious sound. When music is
played, any loud instrument or sound effect is reproduced from the front
speakers, not distractingly located off to the side.
Rear speakers in Music Logic and Music Surround, as in the stereo surround
film effects, are driven by a similar signal to the side speakers, but with some
additional delay and steering. Thus, in a 7 channel setup when a sound
effect is intended to come from the rear, it is reproduced primarily from the
rear speakers with deliberate additional help from the side speakers. (In
THX Cinema and Pro Logic, the rear speakers and the side speakers are
driven in parallel. In the Pro Logic effect, all four side and rear speakers are
driven in mono, and in the THX Cinema effect, there is a decorrelation
between the left and the right, but the signal being reproduced is the same
mono signal used in Pro Logic.)
In the Music Surround and Music Logic effects, the front left and right
outputs are attenuated by the volume and balance controls, but are other-
wise unaltered by the processor. This absence of main front steering is ideal
for playing stereo music, where the original stereo signals are reproduced
from the front speakers with absolutely no alterations. The Music Surround
effect really shines on this material — the center speaker adds a little
stability to the front image without being at all obvious, while the side and
rear speakers add a tremendous amount of ambience. For film, the lack of
steering of the main speakers is noticeable on dialog, and the Logic 7 effect
gives better results.
Lexicon