bias

Bias refers to the operating point of a transistor or tube circuit, and in effects it often appears as a control that alters that setting to change the sound. In fuzz pedals, adjusting bias changes the character of the distortion, from smooth and lush to bright and aggressive¹, or from a sharp drive tone to a thick wall of fuzz². Rolling the Bias back can create a voltage-starved, gated sound³ or a sputtery, ripping velcro tone⁴. Bias tremolo uses an LFO to modulate the bias voltage of amplifier tubes, producing smooth amplitude modulation with mild overdrive from tube saturation⁵, a circuit used in pre-1963 Fender amps⁶ and associated with the Vox sound⁷.