Lexicon 300 - V3.0 REV 1 Owner's Manual page 59

The Algorithms and their Parameters
Note that none of these shape effects are audible unless RTIM is set short
enough. Generally, RTIM 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.
Used with care SHAPE and SPREAD allow the 300 to produce superior
ambience—a sound which is spacious and has great depth—without the long
reverberation of a church.
Random Delays
The Random Hall algorithm in the 300 incorporates random delay elements.
These elements 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 38 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 48 will give an improved sound. WANDER is typically set
to about 10ms at larger settings of SIZE. The effect of WANDER is reduced for
small SIZEs.
Creating a Realistic Sound
When you set out to create a sound, the first and most important decision is how
big a space you want. The best way to start is to listen to several presets and
choose the one which sounds closest to what you have in mind. If necessary, use
SIZE to make a slightly larger or smaller sound, as needed.
Next use RTIM to fine-tune the amount of time the reverberation takes to die
away at the end of musical phrases. Actual halls vary a great deal in their actual
RTIM values. The setting of the BASS is also critical in matching the sound of
an existing hall. An ideal concert hall would have a BASS setting of 1.2. It is rare
when actual physical spaces exceed 1.5. Many (if not most) good recording
environments have values of BASS of 1.0 or less, so a value of 0.8 could be tried
when attempting to match an existing hall.
There are two additional controls to deal with. SHAPE and SPREAD adjust the
effective reverb time when the music is running. Higher values of SHAPE and
SPREAD produce a longer effective reverb time. Longer effective reverb times
give greater spaciousness to the sound.
The 300 reverberation algorithm offers the option of adding early reflections (pre-
echoes) 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.
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