dhcod, I don't know anything about the mm section but when using the mc section I didn't hear much of a difference between settings until I realized there is a small pushbutton on the back of the ear that engages and disengages the transformers. After the button was pushed, there was a big difference in the settings. That same button may have something to do with the mm button or there may be a different pushbutton. They are small and easy to miss