3-4
Algorithms and Parameters
Lexicon
RANDOM HALL (continued)
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
approximately 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.
Random Hall incorporates random delay elements which have
several effects. First, there is a reduction of long-lived modes in the
reverberant decay, which makes the decay less metallic and
reduces the apparent reverb time. The random elements also
improve the steady-state timbre of the program.
The speed at which the delay elements move is controlled by Spin.
Values of Spin which are higher than about 40% can cause audible
pitch wobble in very critical material (such as classical guitar or
piano) and can also cause noise on pure tones. This noise is not
audible in speech, however, and, for mixed music or speech,
values up to 50% will give an improved sound. Wander is typically
set to about 10ms at larger settings of Size. Smaller values of
Wander should be used when smaller Sizes are used.
This algorithm also offers the option of adding early reflections
which have been made into diffused clusters of pre-echoes. The
density of the cluster is set by the Diffusion control. We
recommend that these pre-echoes be used with caution, unless
you are trying to match the sound of the reverberation to a
particular location where such reflections are strong.
An output width control affects the stereo image of the signal
leaving the reverb effect. OutWidth can add width to a signal, or
move a reverb into a surround channel. Either control can be used
statically or dynamically, but in certain positions may be
mono-incompatible.
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