I'm trying to implement this filter in title by following the book "Designing Audio Effect Plug-Ins in C++" By Will Pirkle
Problem I'm facing is the magnitude response error when comparing against analog model of the LP filter. Here is a plot showing the difference.
I get these are values for variables (fc=1000, fs=44100):
>> massberg_test w0 = 0.14248 g1 = 0.045305 gm = 0.70711 wm = 6283.2 Om = 0.071359 Os = 0.10081 g0 = 1.1008 a0 = 0.14612 a1 = 0.055508 b1 = -0.89919 Real: a = [ 0.132736 0.050424 ] b = [ 1.00000 -0.81684 ]
I don't have access to the original paper by M. Massberg so, I can't be sure if the equations in my source book is correct (I've read that the "ac" in g1 formula is just a typo and book errata does not mention other errors for this fileter).
Q: 1. Are the equations found in Pirkle book correct? 2. If 1 is Yes then where to look the issue from?