Here you can define a specific gain for the stereo mic through the GAIN slider. Pay attention not to overdo, or you'll get clipping. The second slider, SPREAD, lets you adjust the panning of your stereo mic. Full left plays it full stereo, that is each of the channel will capture the strokes on its side louder, and just get a glimpse of those played on the other side. Full right value of this slider will blend both channels into a mono version. Adjust the slider in between for your preferred mix.