The ES E output stage consists of the Volume section and the Chorus/Ensemble buttons.
Volume knob: Set the overall output level.
Velo Volume knob: Set the amount (depth) of velocity sensitivity to incoming MIDI note events. When set to higher values, each note is louder, if struck more firmly. At lower values, the dynamic response is reduced, so that there is little difference when you play a note pianissimo (soft) or forte (loud/hard).
Chorus I and II/Ensemble buttons: Turn effect variations on or off. If no button is active, the effects processor is turned off.
Chorus I is a typical chorus effect.
Chorus II is characterized by a stronger modulation.
Ensemble has a fuller and richer sound, due to a more complex modulation routing.