Instrument Plug-Ins : DB-33 : Using the MIDI Learn Function on Avid Virtual Instruments : Invert Range

Invert Range
This option lets you invert incoming MIDI controller data so that the chosen control reacts in inverse proportion to the assigned MIDI controller.
This is useful, for example, when you’re assigning the drawbars in DB-33 to a set of MIDI fader controls, but you want the action to be reversed, so that the faders work like the drawbars on a physical organ.
To invert a control’s response:
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Control-click or Right-click (Mac) or Right-click (Windows) a control, and select Invert Range.