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Notch and Notch Width


arthurs

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It seems to me you're talking about a notch filter. It not something we run into in Hi Fi very much.

The definition appears in the ARRL Handbook (ham radio) under Electromagnitic Interference (EMI).

Notch filter - filter that rejects or suppresses a narrow band of frequecies within a wider band of frequencies.

Looking through the chapter, there is no discussion of it further. However there is a digital notch filter described in the DSP chapter.

Generally, the notch filter is handy when there is a signal at a single frequency which you want to filter out. The filter is not a high pass, or low pass, or band pass. Rather it passes all frequencies except for one very narrow band. Therefore it cuts out a notch in the band.

Filters can be made with various characteristics. Here the major characteristic is the frequency it tunes out. It is possible to adjust the depth of the notch (amount of attenuation) and the width of the notch.

Maybe you're working with a parametric equalizer which also has an adjustable notch filter. A given recording or system might have a 60 cycle hum. You could adjust the notch filter to remove it, and little else.

Gil

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