Empress Effects Phaser - Manual (Page 17)

Expression Pedal Configuration
The pedal ships in this configuration. Plug an expression pedal into
the control port, and use the expression switch to select which
parameter you’d like to control with the pedal. You can select speed
or width when using knob and tap modes. In auto mode the speed
and width switch positions will control sensitivity and release,
respectively. The expression pedal varies the parameter between
zero (or fully counter-clockwise) and the setting on the knob. In
other words, the knob sets the maximum.
Any expression pedal used with the Empress Phaser should have:
Tip - signal
Ring - power
Sleeve - ground
Control Voltage Configuration
In this configuration, width and speed parameters can be controlled
by an external control voltage. The Empress Phaser works with
control voltages which sweep between 0V and 5V.