PEQ

PEQ, short for parametric equalizer, is an audio processing filter that allows selective adjustment of a signal's frequency spectrum. Each parametric band provides three controllable parameters: center frequency (f0), gain (in decibels), and Q (quality factor), which defines the bandwidth around f0. By boosting or attenuating gain at f0, a PEQ can correct problematic resonances, compensate for room acoustics, or sculpt tone for artistic effect. A typical PEQ uses one or more peaking (bell-shaped) filters, though some implementations offer notch, shelf, or high/low-pass shapes.

PEQs come in analog hardware units, digital mixers, and software plugins. Digital PEQs often support multiple bands with precise, automated control and recall, commonly ranging from 3 to 8 bands on a single processor. The design and popularity of the modern parametric EQ were advanced by engineers such as George Massenburg, whose early work in the 1970s helped standardize the form factor and operation; many contemporary devices are marketed as or associated with the "Massenburg EQ."

In practice, PEQs are used for corrective equalization (to flatten some aspects of a room’s response or instrument timbre), creative tone shaping, and feedback management in live sound. They require attention to phase response, as parametric filters introduce phase shifts that can affect transients and stereo imaging when used aggressively or on multiple bands.

See also: equalizer, graphic equalizer, spectral shaping.