A Band-Stop Filter is a filter that removes or attenuates a specific range of frequencies, allowing frequencies both below and above that range to pass through unchanged.

It is the exact opposite of a Band-Pass Filter. It creates a "hole" in the frequency spectrum, being very useful for troubleshooting. Its most common use is to eliminate noise that occupies a specific frequency range, such as an electrical hum or an unwanted resonance from a room or instrument.

Band-Stop Filter vs. Notch Filter

A Notch Filter is, in essence, a Band-Reject Filter with a very narrow bandwidth. It is used to surgically remove a single problematic frequency, while the Band-Reject Filter operates over a slightly wider range.