Empress Effects Nebulus - Manual (Page 6)

The Modes
Chorus A - Basic Chorus Mode: By basic we mean that this chorus is
basically perfect sounding: lush, beautiful, deep, you get the idea.
The special switch allows you to get rid of some of the low
frequency throb that is often associated with chorus effects.
Chorus B - Multi Chorus Mode: This mode offers a rich and thick
multi-tap chorus sound. Again, the special switch allows you to roll
out some of that low frequency throb.
Chorus C - Tremolo Chorus: A blend of chorus & tremolo together.
It's a unique effect that has a great feel. The depth knob controls
the tremolo depth and the special switch controls the chorus.
Vibe A - Single Vibe: This is reminiscent of some of those classic
vibe sounds with some added versatility. In this mode the special
switch controls the resonance intensity.