Lexicon DC-1 Supplementary Manual page 11

DC-1Theory
and Design
8
Ambience Extraction
The Panorama and Surround effects in the DC-1 extract the original acoustic
cues from the recording and present them to the listener from the correct
directions. We call this ambience extraction. The Panorama effect can do this
even with only two loudspeakers. Panorama uses crosstalk elimination to
fool the ear into thinking there is a continuous band of loudspeakers
extending all the way to the sides of the listener. Panorama also supplies a
delayed and filtered L-R signal to rear speakers. On a good recording this
successfully recreates the original recording space, although the ideal
listening area may be small.
The Music Surround and Music Logic effects also provide ambience extrac-
tion. They divide the front energy among three loudspeakers and supply an
ambience signal to the surround loudspeakers. Because a center speaker is
provided, the left and right speakers can be placed far enough to the sides
of the listener to directly excite significant spaciousness, and the resulting
image is wide but seamless. This setup can sound similar to Panorama, and
it works over a large listening area.
Pro Logic, THX Cinema, TV Matrix, Logic 7, and Music Logic also provide
steering. Steering works by enhancing the directionality of the loudest
sound in a mix; it steers the sound out of loudspeakers where it is not needed
and into the ones closest to its direction in the image. In popular music the
loudest sound is usually the vocals, which will be preferentially steered
toward the center loudspeaker. Some steering is frequently beneficial to
music recordings played with a surround speaker arrangement, and it is
essential for films. The latest of the surround programs, Music Logic and
Music Surround, apply the steering in a special way. In these programs
whenever there is no particular loudest sound, the left and right surround
loudspeakers mimic the left and right front loudspeakers, but with added
delay and frequency contouring. This provides an ambience signal with
maximum left and right difference and maximum spaciousness. When
there is a strong signal to the left or right this signal is cleanly removed from
the rear speakers, and reproduced only in the front. The result is a convinc-
ing five or seven channel reproduction of a two channel original recording.
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