« Back to Dictionary Index

Band-stop filter (also known as a band-rejection filter or notch filter) is an electronic filter designed to attenuate (reduce the amplitude of) signals within a specific frequency range while allowing signals with frequencies outside this range to pass through freely.

Key Points about Band-stop Filters:

  1. Functionality:
    • Attenuation: The primary function of a band-stop filter is to attenuate signals within a specific frequency range, known as the stopband.
    • Passbands: Frequencies outside the stopband, both lower and higher, are allowed to pass through with minimal attenuation.
  2. Frequency Response:
    • Stopband: The frequency range within which the filter significantly attenuates the signal. This range is characterized by a sharp drop in the filter’s frequency response.
    • Passbands: The ranges on either side of the stopband where the signal is allowed to pass with little or no attenuation.
  3. Applications:
    • Noise Reduction: Band-stop filters are often used to eliminate unwanted noise or interference within a specific frequency range. For example, they can be used to filter out 60 Hz power line interference in audio equipment.
    • Telecommunications: In telecommunications, band-stop filters are used to remove undesired frequency components from signals, ensuring clear communication channels.
    • Medical Devices: In medical equipment, such as ECG machines, band-stop filters help remove power line interference without affecting the desired signal.
    • Audio Engineering: In audio processing, band-stop filters can be used to remove specific unwanted frequencies from an audio signal, such as a particular hum or buzz.
  4. Types:
    • Notch Filter: A specific type of band-stop filter with a very narrow stopband, designed to attenuate a single specific frequency. This is particularly useful for removing a precise interfering frequency without affecting nearby frequencies.
  5. Design Considerations:
    • Quality Factor (Q): The selectivity of a band-stop filter is often determined by its quality factor (Q). A high-Q filter has a narrow stopband, while a low-Q filter has a wider stopband.
    • Center Frequency: The frequency at the center of the stopband, which is the main target for attenuation.
    • Bandwidth: The width of the stopband, indicating the range of frequencies that will be attenuated.


  • Wi-Fi and Communication Devices: Band-stop filters are used in Wi-Fi routers and other communication devices to filter out unwanted frequencies and prevent interference.
  • Instrumentation: In various types of instrumentation and measurement systems, band-stop filters help eliminate specific frequency noise, ensuring accurate readings and measurements.


Band-stop filters are essential components in various electronic and communication systems, providing the ability to selectively attenuate unwanted frequencies while allowing desired frequencies to pass through. Their application ranges from audio engineering and telecommunications to medical devices and noise reduction in various electronic systems.

« Back to Dictionary Index