Empress Effects Phaser - Manual (Page 9)

Submode 4: Speed Follows Envelope (Random Waveform)
Similar to submode 3 except it uses a random step
waveform. The louder the input signal the more frequently
a new speed value is chosen at random for the effect.
Hitting the tap switch reverses the action so that a louder
signal causes the waveform to slow down.
Submode 5: Follow Trigger
A peak in the volume of the input signal will trigger the
effect to shift from maximum phasing to minimum phasing.
Hitting the tap switch inverts the phasing motion for a
different tone. The LED above the tap switch turns red
when a trigger is detected.
Submode 6: Trigger Random Level
When a trigger is detected the amount of phase is shifted
to a new, random amount. This mode sounds close to a
random waveform, but the changes can be controlled and
triggered by how loud you play your instrument. In this
mode, the release knob determines how quickly it shifts
from the current random level to the next. The attack
toggle has no effect.