Lexicon PCM 90, User Manual

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Lexicon
3-8
PCM 90 User Guide
The Parameters
PCM 90 parameters are organized into labeled rows within each edit matrix.
Although there are similarities among all matrixes, such as having a row of
Controls first, and Modulation, Patching and Custom Control rows last, some of
the parameters within each row, and some entire rows are unique to specific
algorithms.
This section contains descriptions for all PCM 90 parameters, organized
alphabetically by row label as follows:
Compress
Controls
Custom
Delay
Design
Echo
Expand
Modulation
Patches
Spatial EQ
Reflect
Time
Individual parameter descriptions within each row are presented, as far as
possible, in the order in which they appear from left to right in the edit matrix.
Row 4 of the Concert Hall algorithm contains compression controls for a built-
in compressor/expander. Remember that, in some ways, a digital compressor
is the opposite of an analog compressor. An analog compressor reduces gain
when the incoming signal is above a certain threshold; a digital compressor
increases gain when the signal is below the threshold. The end result — lower
dynamic range— is the same, but it's easy to become confused if you are familiar
only with analog equipment.
Ratio
Ratio controls the slope of the gain curve or the ratio of input level versus output
level.
Threshold
Threshold sets the level below which gain is increased. This should normally be
set fairly high (-10dB or more).
Gain
Gain adjusts the gain of low level signals (below the compression threshold).
LookAhead
LookAhead sets the predelay of the audio before the digital VCA. If the source
material has many strong transients, proper adjustment of this parameter can
reduce the possibility of clipping.
Attack
Attack adjusts the attack time constant, determining how quickly the compres-
sor responds to increasing input level. This should normally be set quite low to
allow the compressor to react to sharp transients.
Compress