The Algorithms and their Parameters
youshouidsettheSlZEco~roltoapp~ximatethesizeoftheacou~icspaceyou
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 SSttingS
of the SIZE, SHAP, and SPRD controls. Small acoustic spaces are character-
ized by a rapid buildup of dfffusion. 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.
ROLL sets the frequency above which a 6 dB/octave low-pass filter attenuates
the processed signal. It attenuates both pre-echoes and reverberant sound.
Highfrequenciesareoften rolledoffwiththisparameter, resulting in morenatural
sounding reverberation. The low-pass characteristic can be modffied to a
shelving charactisticwith the SHLF control. When SHLF is off, ROLL is typically
set betwen 2kHz and 4kHz.
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-upof reverberation is gradual, andthe inftial time
gapisusuallyrelativelyshort. NaturalspacesarebestemulatedbysettingSHAP
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 revemerant 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.
RLVL sets the amount of reverberation in the processed signal. It is normally
FULL, but may be reduced for effects where the pre-echoes should dominate.
TDCY sets the frequency above which sounds decay at a progressively faster
rate. ltfiltersallthesoundexceptthepre-echoes. Whenset relativelylow,itgives
adarkertonetothe reverberation, simulatingthe effect of airabsorption in a real
hall. TDCY also helps keep the ambience generated by the program from
muddying the direct sound.
BASS sets the reverb time for low-frequency signals, as a multiplier of the RTIM
parameter. For example, ff BASS is set to 2X, and RTIM is set to two seconds,
the low frequency reverb time will be four seconds. For a natural-sounding hall
ambience, we recommend values of 1 SX or less.
XOVRsetsthefrequencyatwhichthetransitionfrom RTIM toBASStakesplace.
XOVR should be set at least two octaves higherthanthe low frequency youwant
to boost. For example, to boost a signal at 100 Hz, set XOVR to 400 Hz (This
settingworkswellforclassicalmusic). XOVRworks best around4OOforboosting
low frequencies, and around 1.5 kHz for cuffing low frequencies.
ROLL (Hi Freq Roiloff)
PDLY (Pm-Delay)
RLVL (Reverb Level)
TDCY (Treble Decay)
BASS (Baas Muftiply)
XOVR (Bass Crossover)
4-5
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