Lexicon
3-2
PCM 90 User Guide
Random Hall
The Random Hall algorithm gives recorded music a sense of being performed
in a real acoustic location. The Size, Spread and Shape controls allow adjust-
ment of the buildup and decay of the initial part of the reverberation envelope.
Shape controls the shape of the envelope, while Spread and Size set the time
over which this shape is active.
Size acts as a master control for the apparent size of the space being created.
Both Spread and Reverb Time vary linearly with the setting of Size. Thus
maximum reverb time and spread require high settings of Size. To find an
appropriate reverb sound, start with a preset with a similar sound to what you
want to end up with, turn ADJUST to see what effect it has, then investigate the
parameters, starting with Size. Until you are familiar with the PCM 90, we
recommend that you edit any patch driving a parameter rather than editing the
parameter directly.
Once a size has been selected, Spread and Shape are used to adjust the shape
and duration of the initial reverb envelope, which together provide the major
sonic impression of room size.
When Shape is at minimum, the reverberation envelope builds up very quickly
to a maximum amplitude, and then dies away quickly at a smooth rate. This
envelope is characteristic of small reverberation chambers and reverberation
plates. There are few (if any) size cues in this envelope, so it is ineffective in
creating ambience. With this Shape setting, Spread has no effect. The density
is set by the Size control, and the rate of decay is set by the reverb time controls.
As Shape is raised to about 1/8 of its range, the initial sharp attack of the
reverberation is reduced, and reverberation builds more slowly. The envelope
then sustains briefly before it begins to die away at the rate set by Mid Rt. Spread
has little or no effect on this shape. When Shape is at 1/4 of its range, buildup
is even slower and the sustain is longer. Now Spread affects the length of both
the buildup and the sustain. As a rough estimate, the sustain will be approximate-
ly the time value indicated by the Spread display (in milliseconds).
As Shape is raised further, the buildup and sustain remain similar, but now a
secondary sustain appears in the envelope, at a lower level than the first. This
secondary plateau simulates a very diffused reflection off the back wall of a hall,
and is effective in creating a sense of size and space. This reflection becomes
stronger and stronger, reaching an optimal loudness when Shape is at about 1/
2 of its range.
The highest Shape settings are typically used for effects. Near the top of the
scale the back wall reflection becomes stronger than the earlier part of the
envelope, resulting in an inverse sound.
Note that none of these shape effects are audible unless Mid Rt is set short
enough. Generally, this control should be set to a value of about 1.2 seconds for
small rooms, and up to 2.4 seconds or so for halls. Size should also be set to a
value appropriate to the desired hall size (note, however, that small sizes color
the reverberation).15 meters makes a very small room, and 38 meters is useful
for a large hall.
Summary of Contents for PCM 90
Page 1: ...User Guide Digital Reverberator PCM 90...
Page 3: ...User Guide Digital Reverberator PCM 90...
Page 11: ...1 1 Product Overview 1 Product Overview Block Diagram...
Page 84: ...Lexicon 3 24 PCM 90 User Guide...
Page 112: ...4 28 PCM 90 User Guide Lexicon...
Page 122: ...5 10 PCM 90 User Guide Lexicon...
Page 129: ...Lexicon Part 070 10399 Rev 1...
