thumb|250px|Digital domain parametric equalisation
An audio filter is a frequency-dependent circuit, working in the audio frequency range, 0 Hz to 20 kHz. Audio filters can amplify (boost), pass or attenuate (cut) some frequency ranges. Many types of filters exist for different audio applications including hi-fi stereo systems, musical synthesizers, effects units, sound reinforcement systems, instrument amplifiers and virtual reality systems.
Types
;Low-pass
:Low-pass filters pass through frequencies below their cutoff frequencies, and progressively attenuate frequencies above the cutoff frequency. Low-pass filters are used in audio crossovers to remove high-frequency content from signals being sent to a low-frequency subwoofer system.
;High-pass
:A high-pass filter does the opposite, passing high frequencies above the cutoff frequency, and progressively attenuating frequencies below the cutoff frequency. A high-pass filter can be used in an audio crossover to remove low-frequency content from a signal being sent to a tweeter.
;Band-pass
:A band-pass filter passes frequencies between its two cutoff frequencies while attenuating those outside the range.