bandstopfiltre

A bandstop filter, also known as a notch filter or band-rejection filter, is an electronic filter that passes signals within a certain frequency range but attenuates, or stops, signals at specific frequencies while allowing others to pass through. This is the opposite of a bandpass filter, which allows a specific range of frequencies to pass. The defining characteristic of a bandstop filter is its "stopband," the range of frequencies that are significantly attenuated.

Bandstop filters are commonly used to remove unwanted frequencies from a signal. A classic example is the removal of a specific hum frequency, such as the 50 Hz or 60 Hz power line hum that can interfere with audio signals. In telecommunications, they can be used to eliminate interference from adjacent channels. In audio processing, they are employed to reduce or eliminate specific problematic frequencies, like feedback tones.

The design of a bandstop filter can be achieved using various circuit configurations. These include passive filters, which use only resistors, capacitors, and inductors, and active filters, which incorporate amplifying components like operational amplifiers. The sharpness and depth of the stopband are determined by the filter's order and component values. A narrow and deep stopband is often desirable for precise frequency removal, while a wider stopband might be used for broader noise reduction. The transition from the passband to the stopband and back to the passband is characterized by the filter's roll-off rate.