Audio filter

Audio filters can amplify (boost), pass or attenuate (cut) some frequency ranges.

In more complex cases, an audio filter can provide a feedback loop, which introduces resonance (ringing) alongside attenuation.

Audio filters can also be designed to provide gain (boost) as well as attenuation.

In other applications, such as with synthesizers or sound effects, the aesthetic of the filter must be evaluated subjectively.

Self-oscillation occurs when the resonance or Q factor of the cutoff frequency of the filter is set high enough that the internal feedback causes the filter circuitry to become a sine tone sine wave oscillator.