Rocktron VooDu Valve Online User Manual page 27

The TREMOLO function is available only in configurations displaying "TREM" in the
configuration title.
The Tremolo effect continuously varies the volume of the signal.
The PARAMETER SELECT control will allow you to access these TREMOLO parameters:
TREMOLO The TREMOLO I/O parameter determines whether the Tremolo is
active or bypassed for the current preset.
LOCATION The LOCATION parameter determines whether the Tremolo is located
Pre-Reverb or Post-Reverb. Most vintage amplifiers configured the
Tremolo (or vibrato) Post-Reverb.
DEPTH The DEPTH parameter determines the amount of modulation for the
Tremolo signal. Lower DEPTH settings produce more subtle tremolo
effects, while higher settings will result in a more extreme tremolo
effect.
RATE The RATE parameter determines the speed at which the tremolo signal
modulates (or increases and decreases in volume).
SHAPE The SHAPE parameter determines the waveshape of the tremolo signal.
Selecting a different waveshape produces a different tremolo effect.