The contour seems to matter little when I'm in the "Normal" input. The bass control, however is profound!!. I can't even switch on the bass boost. It's too bassy. The "bright" channel seemd to be much more balanced, tone wise. The contour seems to fill in some mids there. I only have tested the amp with my Sonic 1-18 so far. Maybe with a 4-10 it might be more balanced in the "normal" channel. Any experience with this "Contour" knob.??