[Kst] [Bug 87446] Butterworth filters are miss-named.

Andrew Walker arwalker at sumusltd.com
Thu Aug 19 01:08:58 CEST 2004

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------- Additional Comments From arwalker sumusltd com  2004-08-19 01:08 -------
Hi Barth,

As I understand it (and its quite possible I don't) a Butterworth lowpass filter is defined by:
H = 1/(1+(D+D_0)^2n), where D_0 is the cutoff frequency and n the order. (Such a filter is preferable to a rectangular response function in the frequency domain as it prevents some unpleasent side-effects like ringing).
It is possible to generate causal code (such as given in the website you link to) to approximate a Butterworth filter. This is desirable for situations where you don't want to store all the preceeding values; of particular importance in linear circuits.
I think what we have is a Butterworth filter. If it isn't why would we refer to it (as you suggest) as a '0 phase butterworth' in the description.

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