In Reason, send the signal in via the additional inputs on the back of the device: In Logic, it's selected in the top right of the plugin window:
In Ableton Live, this is selected with the Device Window, as shown: For more help using Reveal watch our video here. Here are a few examples of how to do that in different DAWs once you have placed the plugin on the track you wish to be affected by the ducking.
FAST Reveal uses one audio signal to affect another, and so when using it you'll need to tell the plugin which signal should be used to cause the affected track to duck.
