Equalizer parameter control interface and method for parametric equalization

A parametric equalizer has an audio filter with a plurality of electronic components. A first control knob ( 32 ) controls a center frequency of the audio filter. A second control knob ( 34 ) jointly controls signal level and bandwidth of the audio filter. The second control knob uses a potentiometer ( 120 ) with variable resistive elements on a common shaft ( 122 ). The variable resistive elements ( 56, 110 ) are coupled to nodes within the audio filter to jointly control the signal level and bandwidth. The control knobs are mounted to a control panel ( 30 ) for user access. A musical instrument, such as an electric bass guitar, generates audio signals, which are routed to a pre-amplifier ( 16 ) containing the parametric equalizer. The equalizer conditions the audio signals, which are boosted with a power amplifier to drive a speaker system.