I'm trying MIM (Magnitude Invariance Method) and PIM (Phase Invariance Method) for to improve biquad LPF response at low sampling rates. I'm looking some help and examples of usage if available.
EDIT_1: I tried MIM method for 2nd order
LPF fs=44100 fc=15000 Q=0.707
Peak filter fs=44100 fc=10000 Q=0.707 db=6
Here are the resulting plots:
Responses looks promising.
Example code (LPF):
% Analog model for LP filter: fs = 44100; fc = 10000; Q = 0.707; w0 = 2 * pi * fc; b2 = w0^2; a2 = [1 w0/Q w0^2]; Ds = tf(a2, b2); % Calculate coefficients using MIM [Dz] = c2dn(Ds, fs, 'mim', 2, 4096*256); bodemag(Ds, 'r', Dz, 'b');