Gain controls the level of signal amplification within a circuit, determining how hard the signal is driven into the next stage. Increasing gain raises the input level and can introduce overdrive, distortion, or fuzz as the signal is pushed beyond clean headroom.

It plays a central role in shaping tone, affecting sustain, saturation, and overall feel. Low gain settings tend to preserve clarity and dynamics, while higher gain settings create thicker, more compressed sounds commonly used in rock, metal, and lead playing.