hello
here you are my friend !
tried to fit minimum size IIR filter first , then FIR coefficients are equal to impulse response to IIR
data = importdata ('plate_tf.mat');
freq = data.Hz; % frequency
frf = data.com; % FRF complex
% IIR model
Fs = 1e3;
W = linspace(0,pi,length(freq));
ind = find(freq>50 & freq <150); % frequency weighting ; data reliable between 5 and 80 Hz
WT = zeros(size(W));
WT(ind) = 1;
NB = 2;
NA = 2;
[B,A] = invfreqz(frf,W,NB,NA,WT,Fs);
% check bode plots
[H,WW] = freqz(B,A,length(frf));
figure(1),
subplot(2,1,1),plot(freq,20*log10(abs(frf)),'b',freq,20*log10(abs(H)),'r');grid
subplot(2,1,2),plot(freq,180/pi*(angle(frf)),'b',freq,180/pi*(angle(H)),'r');grid
% Impulse response
[FIR,X] = dimpulse(B,A);
samples = length(FIR);
time = 1/Fs*(1:samples);
figure(2),
plot(time,FIR,'r');grid
title('Impulse response (FIR model)')
xlabel('Time (s)');
ylabel('Amplitude')
