When the red light turns on for distortion is when it does the overlap. Its not the dd1. The dd1 you used a tone to set the overlap and when it went to distortion you turned back till light off. Dd1+ when it hits distortion and you press the overlap button, you are essentially doing the same but without a tone on a disk. Cant set overlap without the distortion light on. When the light comes on thats distortion at 40hz 0db. When you hit the button you can go to -15db. I did -5db on my amps