Darkglass Microtubes B3K 2.0 Bass Distortion Pedal Tone: Controls the high frequency content of the sound. A variable low pass filter from 3kHz (ccw) to 8kHz (cw). Blend: Mixes the clean input signal with the overdriven signal. The clean signal remains at unity gain while the volume of the overdriven signal is set by the Level knob, allowing for fine control of the blend ratio. Drive: Sets the amount of saturation in the overdriven signal. Grunt Switch: When engaged provides a massive low end boost to really thicken your sound. Mid Boost: Gives a subtle 6dB boost from 300 Hz to 1kHz to help you cut through a bit more.