Keeley Stahlhammer Distortion Pedal with 2 Clipping Modes Made in the USA! Bass  This is for your low end response, around 100Hz and lower. Middle  This affects frequencies from 800Hz to about 1.6KHz. You can heavily scoop out the mids, or push them to really stand out! Treble  This is to roll of treble or push upper frequencies around 3.2KHz and higher. Gain Switch  Two modes of distortion are available from switch mounted on the right hand side of the pedal.