文件名称：What is notch filter
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更新时间：2016-07-02 08:31:50
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A Notch filter is a filter that passes all frequencies except those in a stop band centered on a center frequency. A closely related Knowledgebase item discusses the concept of the Q of a filter. This Knowledgebase item focuses on high Q notch filters - the type that eliminate a single frequency or narrow band of frequencies. A closely related type of filter - a band reject filter, is discussed in a separate knowledgebase item. The amplitude response of a notch filter is flat at all frequencies except for the stop band on either side of the the center frequency. The standard reference points for the roll-offs on each side of the stop band are the points where the amplitude has decreased by 3 dB, to 70.7% of its original amplitude.