Lexicon CP-1 PLUS V2.0 Owner's Manual page 62

CP-1 Digital Audio Environment Processor
side-channel sibilants by narrowing the spread of the front channels in the
presence of dialog; this compromise is unnecessary in the CP-1.
The CP-1 Decoder
The CP-1 decoder is unusual in a number of ways. First of all, the Dolby
Surround decoding is entirely digital. (Many surround decoders are
advertised as "digital" because there is a digital delay line for the surround
channel, but the matrix and the logic decoding are done in analog.)
Because the Pro Logic decoding is all digital, we can use some of the digital
memory to delay all the output channels by 20 milliseconds — about the
same as the acoustic delay you get in the front row of a theater. (The
surround channel is delayed by an additional 16 to 32 milliseconds.) This
delay allows plenty of time for the CP-1 to determine the direction of sounds
and adjust the matrix before the sounds are sent to the amplifiers. This
substantially improves dialog and effects cancellation, as is immediately
apparent from the spread of ambient material or music, even in the presence
of dialog.
The CP-1 can also sense and continuously correct both balance and azimuth
errors in the incoming material. All the time the film is playing, the CP-1 is
checking balance and azimuth, keeping the dialog perfectly centered. The
result is superior steering. An added benefit is that the CP-1 needs no front
panel input balance control; the user need not bother with this adjustment.
You can check the quality of the balance and azimuth in a tape or disc if you
wish by turning the Auto Azimuth/Balance parameter off and observing
any changes in the location of dialog and effects.
In addition, because the side and rear cancellation of dialog is unusually
good even with poor material, you can use Stereo Logic to set the rear
channel filtering higher than is recommended in the Pro Logic specifica-
tions. This added surround brilliance makes some effects, such as falling
rain all around you or objects zooming from rear to front, much more
convincing. This feature should be used with caution, however, since in this
mode the decoder is different from the one on which the film was mixed.
Since films are orinally recorded for playback in commercial theaters, the
treble is boosted to compensate for the high frequency loss caused by the
movie screen and the listener's distance from the speakers. In the home, the
speakers are not behind a screen, and we generally sit only 10-15 feet from
these speakers. Under these conditions, many films will sound too bright.
The Film EQ parameter compensates for this exaggerated treble and should
be used for any Dolby surround encoded films. Television shows and Dolby
surround encoded music are usually mixed for home playback and so do
not have the treble boost. In these cases, turn the Film EQ off.
Theory
Design
Pro Logic decoders remove dialog
from the left and right channels,
while maintaining stereo as much as
possible.
Pro Logic requires phase accuracy.
Common azimuth errors cause ghost
dialog in all channels unless the azi-
muth error is corrected.
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