The classic Double Muff is an overdrive/fuzz, which consists of 2 Muff Fuzz circuits cascaded (whatever that means) into each other. The controls are very simple (and that's one of the things that makes this pedal so much fun to use for me), there's only one knob for each circuit, which adds volume and gain together, and a switch that lets you choose between using only one circuit (which gives a nice mid-boosting overdrive) and using both. When using both, one of them acts more like a volume control, and the other adds gain. You can get into fuzz territory when using both circuits together. Another nice feature is that you can clean the sound up A LOT using only the volume of the guitar. Then there's one issue, this pedal has to be the first in chain to sound good (even before a true-bypass tuner), if there's anything between the pedal and the guitar, you're in treble hell.