带阻滤波器

信号处理中的带阻滤波器是指能通过大多数频率分量、但将某些范围的频率分量衰减到极低水平的滤波器，与带通滤波器的概念相对。其中点阻滤波器（notch filter）是一种特殊的带阻滤波器，它的阻带范围极小，有着很高的Q值（Q Factor）。

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 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

RF example 1: Non-linearities of power amplifiers For instance, when measuring non-linearities of power amplifiers a very narrow notch filter could be very usefull to avoid the carrier so maximun input power will not be exceeded.

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线性滤波器

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