Frequency Response of Low Pass Bessel Filter.
The Poles of the Bessel filter can be found by solving a polynomial in s.
The maths used here can be found in C. Britton Rorabaugh - Digital Filter
Designer's Handbook - Publ by Mc Graw Hill.
There are 2 possible approximations. The first applet shows the case
where the poles are chosen to produce an attenuation of 3dB at
w = 1. The second applet shows the case where the
poles are chosen for normalised group delay.
Magnitude is shown by red and pink lines, phase shift by green line
and group delay by cyan line.
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COPYRIGHT © 2005 Cuthbert Nyack.