Lexicon DC-1 Supplementary Manual page 30

DC-1 Theory
and Design
DC-1 Digital Controller
The decoding works by combining very high quality standard Pro Logic
decoding with the technology of the Music Logic program. The front
channels (left, center, and right) are decoded with standard Pro Logic, but
with the addition of an adjustable delay for the center channel. The two rear
channels operate in a dual mode. When the film surround content is
primarily music or ambience, the rear channels maintain full stereo, repro-
ducing the left and right front channels with the addition of frequency
contouring and delay. (In the TV mode the contouring is adjustable —
allowing full bandwidth surround if desired.) When the front hemisphere
contains steered information, such as dialog or sound effects, these signals
are cleanly removed from the stereo surrounds. Thus, dialog and all on-
screen sound effects remain in the front where they belong. The new
decoding depends critically on our ability to remove unwanted sound from
the stereo surrounds, and this would not be possible without the accuracy
afforded by our Auto Balance and Auto-Azimuth circuits.
As sound effects move toward the rear, the processor decodes differently.
Effects which move from left to rear pan smoothly from the left front
loudspeaker to the left side, and then from left side to both left and right rear
loudspeakers. Effects which pan from right to rear behave similarly. Once
full rear is reached, the decoder outputs are identical to a standard Pro Logic
decoder, so full compatibility is maintained. The action of the decoder has
been extensively tested both at Lexicon and at Lucasfilm to ensure the intent
of the film director is accurately reproduced.
Although films have not yet been deliberately mixed to take advantage of
the capabilities of the new decoding, the improvement on standard films
can be dramatic. The improvement in spaciousness with music and ambi-
ence is obvious. On films with aggressive sound effects the combination of
surround steering and localization can convince listeners they are listening
to a true discrete surround mix.
Based on Dolby AC-3, an audio encoding technology developed by Dolby
Dolby Digital
Laboratories, Dolby Digital delivers six discrete channels of digital sound.
Five channels: Left, Center, Right, Left Surround and Right Surround are
full-range (3Hz to 20,000Hz). The sixth channel is called the Low Frequency
Effects (LFE) channel. It can contain additional bass to emphasize the
impact of scenes such as explosions or crashes. Because the LFE channel has
a limited frequency response, it is often referred to as the ".1" channel. When
added to the five full-range channels, the Dolby Digital surround system is,
therefore, commonly referred to as having "5.1" channels.
As all channels are discrete digital tracks, channel separation and dynamic
range are greatly improved over analog surround sound. One advantage is
a dramatic improvement in localization of dialog. In addition, full-range
surround effects can be independently directed to left surround or right
surround speakers for a heightened sense of realism. Another benefit is
increased dynamic range, which allows subtle audio cues to be more easily
heard while giving loud effects, such as explosions, life-like impact.
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