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CP-1 Digital Audio Environment Processor
sides. Both methods depend on having the added sound come from a
different direction than the original music, and each method has some
advantages. With either method of generating SI there is an additional
choice the CP-1 allows the user to make: the sideways energy cues of the
original recording can be extracted by the CP-1, or a different hall sound can
be generated and supplied from the correct directions.
Ambience Extraction
The Panorama and Surround programs in the CP-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 three Panorama
programs can even do this 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 and 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 Surround programs, Stereo Logic and Pro logic, also work by ambience
extraction. They divide the front energy among three or more loudspeakers
and supply a delayed and filtered difference signal to rear 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 SI
and the resulting image is wide but seamless. This set-up can sound similar
to Panorama, and it works over a large listening area.
Stereo Logic and Pro 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 loud-
speaker. Some steering is frequently beneficial to music recordings played
with a surround speaker arrangement, and it is essential for films.
Ambience Generation
The Reverb and Ambience programs in the CP-1 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 programs the original stereo channels are pre-
sented unaltered to the main loudspeakers, and new signals are generated
for the side and rear loudspeakers. Both Ambience and Reverb can be
configured to use a version of Panorama to generate the correct side sound
even when side loudspeakers are absent. In this mode the side signals are first
passed through Panorama before being mixed into the main loudspeakers,
so the resulting hall sound is perceived as coming from the side and is well
separated from the original sound.
Theory
Design
The confusing frontal reflections can be ab-
sorbed leaving the essential lateral ones. This
is better, but not ideal.
With the CP-1, confusing short reflections can
be absorbed; the CP-1 will supply the essential
lateral sound - which can simulate a much
larger space.The more absorbent the playback
room, the better it will sound, and the closer it
will sound to a real hall, or larger environment.
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