Lexicon PCM 90 - REV 1 User Manual page 73

The Algorithms and Their Parameters
Attack
Attack is provided in the Plate algorithm to set the sharpness of the initial
response to an input signal. High settings cause an explosive sound, while low
settings cause the sound to build up more slowly with time. Attack only affects
the level of sound within the first 50 milliseconds.
Shape, Spread
In Random Hall, Concert Hall and Chamber/Room, Shape and Spread work
together to control the overall ambience of the reverberation. Shape determines
the contour of the reverberation envelope. With Shape all the way down,
reverberation builds explosively, and decays quickly. As Shape is advanced,
reverberation builds up more slowly and sustains for the time set by Spread. With
Shape in the middle, the build-up and sustain of the reverberation envelope
emulates a large concert hall (assuming that Spread is at least halfway up, and
that Size is 30 meters or larger). Low Spread settings result in a rapid onset of
reverberation at the beginning of the envelope, with little or no sustain. Higher
settings spread out both the buildup and sustain.
Def
In the Concert Hall algorithm, Definition affects the echo density buildup rate
during the latter part of the decay period. When set to Off, the rate is determined
by the program material. Raising Definition through its range (1-99%) causes the
sound to become choppier — the decrease in echo density creates increasingly
distinct, repetitive echo trails.
Depth
In the Concert Hall algorithm, Depth sets the output amplitude envelope,
changing the listener's perspective from the front to the rear of the hall.
Spin
Spin affects the movement of the reverberation tail. The object of Spin is to
continuously alter the timbre of the reverberant sound. This makes the result
more natural, without making the position of instruments unstable. Spin should
typically be set to values between 10% and 50%. Higher values may make the
timbre of piano or guitar unstable.
Chorus
In the Concert Hall algorithm, Chorus randomizes delay times and introduces
modulation to make reverberation sound less metallic. Increasing Chorus
increases the rate of modulation. Because Chorusing can cause pitch variation,
this parameter should be set with care when using sources with very little pitch
wobble (such as guitar or piano). A good practice is to increase the setting until
pitch wobble becomes noticeable, then lower it slightly.
Link
This control is available in all algorithms except Ambience. When Link is set to
On, the reverb time (Mid Rt) and Spread scale linearly as the Size control is
varied. For some special effects, Mid Rt, Spread and Size can be unlinked.
High Cut
High Cut sets the high frequency cutoff of a low-pass filter. This parameter
affects both channels.
3-13