In signal processing, a band-stop filter or band-rejection filter is a filter that passes most frequencies unaltered, but attenuates those in a range to very low levels. It is the opposite of a band-pass filter. A notch filter is a band-stop filter with a narrow stopband (high Q factor).
Other names include 'T-notch filter', 'band-elimination filter', and 'band-rejection filter'.
Typically, the width of the stopband is less than 1 to 2 decades (that is, the highest frequency attenuated is less than 10 to 100 times the lowest frequency attenuated). In the audio band, a notch filter uses high and low frequencies that may be only semitones apart.
Audio example 1: Anti-hum filter
- Low Freq: 59 Hz
- High Freq: 61 Hz
This means that the filter passes all Band-stop filter frequencies, except for the range of 59–61 Hz. This would be used to filter out any noise from a 60 Hz power line.
Audio example 2: Anti-presence filter
- Low Freq: 1 kHz
- High Freq: 4 kHz
References
- Federal Standard 1037C
- MIL-STD-188
Electronics Topics
The field of electronics is the study and use of systems that operate by controlling the flow of electrons or other electrically charged particles in devices such as thermionic valves and semiconductors. The design and construction of electronic circuits to solve practical problems is part of the fields of electronic engineering, and the hardware design side of computer engineering. The study of new semiconductor devices and their technology is sometimes considered as a branch of physics.
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