What is a Notch Filter?

A notch filter is a type of audio filter designed to remove or significantly reduce a very narrow range of frequencies from an audio signal while leaving the rest of the sound largely unaffected.

Unlike broader filters that affect large sections of the frequency spectrum, a notch filter targets a specific problematic frequency, such as electrical hum, feedback, or resonance. By cutting only that narrow band, the overall tone of the audio can remain mostly unchanged.

Notch filters are commonly used in audio mixing, sound reinforcement, broadcast systems, and audio restoration to eliminate unwanted noise or ringing frequencies. For example, they are often used to remove 50 Hz or 60 Hz power hum, feedback frequencies in live sound, or resonant tones in recordings.