Notch Filter

There’s no notch filter other than the download one, right? Nothing built-in?

You can put notch commands into the Nyquist prompt, (no plug-in required) …

To eliminate one narrow band of frequencies one uses a so-called “notch” filter (named for the fact that it makes a notch in the frequency spectrum).
To do this with Audacity, click on Effect > Nyquist Prompt and enter the following code:

(notch2 s 4255 50)

For stereo tracks you’ll have to use a slightly more complicated code:

(vector (notch2 (aref s 0) 4255 50) (notch2 (aref s 1) 4255 50) )

This line tells Nyquist to process the notch filter on both channels.

Substitute “4255” with the frequency that you identified in your own spectrum. That other number, 50 in this example, is the Q factor of the filter. You might find that you need to experiment with it. Varying this value influences the width and depth of the notch. A lower value makes for a wider and deeper notch and vice-versa - just experiment a bit.

i.e. the Q value is anti-intuitive: small Q gives a big wide notch, big Q produces a narrow notch.

[However IMO David Sky’s notch flter plugin is easier to use]

Yes, I know what the Q or Quality of a notch is. Basically the ratio of peak to width. Excellent. Turns out I didn’t need it, but it was a close call. I had a damaged clip with a consistent peak of garbage around 15,000 Hz.

Thank you.


Not currently, but Bill and I proposed including one.
Gale seemed to be in favour of including it in Audacity 1.3.13 beta, though I don’t know if there has been any “official” approval as yet.
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