Lexicon PCM 90 - REV 1 User Manual page 83

The Algorithms and Their Parameters
Shelf
In Random Hall, Shelf modifies the lowpass characteristic of Rt HC, turning it into
a shelving filter. Shelf sets the gain of an output patch which is mixed with the
output of Rt HC to form the main reverberant output. Both the pre-echoes and
the reverberation are affected. For example, if Shelf is set to -6dB, frequencies
below approximately Rt HC/2 will be boosted by 3.5dB. Above approximately Rt
HC/2, the response will be flat.
Shelf provides a method for making the spectral content of the reverberation
match the ideal spectrum for musical acoustics in rooms. For this application, Rt
HC should be set between 700 and 1.5kHz, with Shelf set between -12 and -6dB.
Decay
In Ambience, Decay controls the length of the ambience "tail".
Decay Lvl
In Ambience, Decay Lvl controls the level of the ambience "tail". When Decay
Lvl is off, ambience consists entirely of the early reflection signal.
Dry Dly
Dry Dly is used to add fine control to Ambience. An additional dry path is created
"inside" the ambience effect. When necessary, this path can be delayed slightly
to match an ambience.
DryDlyMix
In Ambience, DryDlyMix is used to control the relative levels of the internal dry
path and the ambience effect itself. A value of 100% indicates a completely dry
path. This is identical to the normal external dry path, except that it is delayed
by DryDly. If this control is used to vary the wet/dry mix, it is recommended that
the value of Mix on the Controls row be set to 100%.
Infinite
In the Room algorithm, this control is provided to turn the Infinite effect On or Off.
3-23