Empress Effects Phaser - Manual (Page 5)

Auto Mode
In auto mode, the effect parameters are changed based on how you
are playing. The changes follow the envelope of the input signal, or
are triggered by sudden changes in the signal volume.
Effects parameters are changed in one of two ways when you use
auto mode:
1. Envelope Follower
When following an envelope in auto mode, the pedal tracks
the input volume and changes a parameter to follow the
changes in the volume level. The envelope follow approach
is used in submodes 1 through 4.
2. Trigger Detection
When detecting a trigger in auto mode, the pedal tracks the
signal and when a sudden, rapid increase in volume occurs,
it changes the parameter from a low to high value. The kind
of actions that would set off a trigger might be an
aggressive strum on a guitar or a chord hit on a Rhodes. The
trigger detection approach is used in submodes 5 and 6.