Below is a classic tone stack from the Big Muff distortion pedal. Basically, it’s a pair of filters whose output is combined through the 100k mix pot. The 39k/.01 filter attenuates the highs and only passes low frequency. But, the 3900pF/22k filter does the opposite.

Big Muff Distortion Pedal Tone Control circuit schematic

This filter passes the high frequency and filters out the lows. The 100k pot blends together the signal from each filter and acts as a tone control. The values of vintage Muff pedal are shown here. Even on that classic box, the values sometimes varied slightly. [Circuit’s schematic diagram source: muzique.com]