Voice: Gives you three tonal differences; MOSFET, Silicon and Normal. These options give you different levels of compression when adding gain, and really change the overall character a lot. The Normal setting has little to no compression if that is desired.
Normal/Bright: Works great when using either darker humbuckers—switch to Bright, or if using single coils, keep it normal. Using the master tone control in conjunction with this switch gives you a lot of useful variation.
Bandwidth: What a traditional Tube Screamer lacks—here, the Dunes gives you the option of adding a lot of deep low end—great for single coils, or switch it back to the more traditional screamer mode, accentuating the midrange, with less emphasis on the bottom end."
PCB and schematic available on PedalPCB website here.