Lexicon 300 - V3.0 REV 1 Owner's Manual page 83

Split Chamber Adjustments Page 1
RTIM sets the reverb time for mid-frequency signals. Because low-frequency
reverb time (BASS) is a multiplier of RTIM, RTIM acts as a master control for the
reverb time.
SIZE sets the rate of buildup of diffusion after the initial period (which is controlled
by DIFF). It also acts as a master control for RTIM and SPRD. The SIZE control
changes a reverb sound from very large to very small. Generally, you should set
the SIZE control to approximate the size of the acoustic space you are trying to
create, before adjusting anything else. The size in meters is roughly equal to the
longest dimension of the space. Moving SIZE while a signal is present may
cause audible transients on critical material.
The apparent size of the space created is actually a combination of the settings
of the SIZE, SHAP, and SPRD controls. Small acoustic spaces are character-
ized by a rapid buildup of diffusion. However, both small and large spaces
frequently have an uneven buildup of initial reverberation. This uneven buildup
is controlled by the SPRD and SHAP controls.
PDLY adjusts an additional time delay between the input of signal and the onset
of reverberation. The control is not intended to mimic the time delays in natural
spaces. In real rooms the build-up of reverberation is gradual, and the initial time
gap is usually relatively short. Natural spaces are best emulated by setting SHAP
at a middle value and adjusting SPRD for the desired effective pre-delay.
Additional delay added with the PDLY control can increase the initial time gap
slightly, emulating a situation where reverberant pick-up microphones are
located much further from the source than the main microphones. If less than
about 30ms of pre-delay is added, this additional delay can add clarity with some
music, but it can also sound unnatural. Large pre-delays can be useful for slap-
echo effects.
TDCY sets the frequency above which sounds decay at a progressively faster
rate. It filters all the sound except the pre-echoes. When set relatively low, it gives
a darker tone to the reverberation, simulating the effect of air absorption in a real
hall. TDCY also helps keep the ambience generated by the program from
muddying the direct sound.
SHAP and SPRD work together to control the overall ambience of the reverbera-
tion created by the 300. SHAP determines the contour of the reverberation
envelope. With SHAP all the way down, reverberation builds explosively, and
decays quickly.
As SHAP is advanced, reverberation builds up more slowly and sustains for the
time set by SPRD. With SHAP in the middle, the buildup and sustain of the
reverberation envelope emulates a large concert hall (assuming that SPRD is at
least halfway up, and that SIZE is suitably large—30 meters or larger.)
The Algorithms and their Parameters
RTIM (Mid-Frequency
Reverb Time)
SIZE
PDLY (Pre-Delay)
TDCY (Treble Decay)
SHAP (Shape)
4-27