When you use the D-fx Chorus plug-in in Stereo mode, a Sum Inputs button appears next to the right channel Input Level slider. Clicking the Sum Inputs button sums the source input signals (regardless of whether the input is mono or stereo) before processing them.The source signal then appears in the center of the stereo field, and the processed signal is output in stereo. When you click the Sum Inputs button, the LFO waveform on the right channel is automatically phase inverted to enhance the mono-stereo effect.