Lexicon CP-1 Theory Of Operation page 12

Multi-Channel Music & Cinema Systems
Theory and Design
Ambience Extraction
The Panorama and Surround effects 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 the three front 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.
Ambience Generation
The ambience and reverb effects — Nightclub, Concert Hall, Church and
Cathedral — synthesize the side and rear sound of several different acoustic
spaces. Rather than extracting the acoustic cues of the original hall from the
recording, they generate a new environment, effectively enlarging and
improving the acoustics of your listening room. In these effects the original
stereo channels are presented basically unaltered to the main loudspeakers,
and new signals are generated for the side and rear loudspeakers.
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