Alesis QuadraSynth Plus Reference Manual page 89

Editing Programs: Chapter 6
appear to have two zones. All notes from the bottom of the
keyboard to the high limit note will play, and all notes from the
lower limit to the top of the keyboard will play, but the notes
between the high limit and the lower limit will not play. This can
be further enhanced in Mix Mode by using the Range function in
Mix Edit Mode to cap-off the lower and high limits.
QuadraSynth Plus Piano Reference Manual 90