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Design IIR filter from absorption data

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Marius Tøndel Eliassen
Marius Tøndel Eliassen on 15 Feb 2020
Hello!
As the title says, and I have got the coefficients. This:
f = [125 250 500 1000 2000 4000];
alpha = [0.09 0.2 0.5 0.7 0.8 0.9];
N = 1; % Filter order
Fs = 44100 % Sampling frequency
w = f/fs*2*pi; % Frequency in radians
R = sqrt(1-alpha);
% Find R(z) coefficients:
[b,a] = invfreqz(R,w,N,N);
How do I go about from here, as I need to visualize the filter, e.g. a plot of the magnitude response?
Best regards,
Marius

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Answers (1)

Kaashyap Pappu
Kaashyap Pappu on 24 Feb 2020
The fvtool could be what you are looking for. It will allow you to do the necessary visualizations.
Hope this helps!

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Marius Tøndel Eliassen
Marius Tøndel Eliassen on 24 Feb 2020
That seems a good option for visualization. However my issue now is that my code doesn't give me a realistic filter shape for my coefficients. It should look like a low pass filter, but it is instead giving me something that looks like a shelving filter. It might be something I am missing in that code. What I am trying to do is depicted in the last section before the 3.1 mark in this article. Figure 1 shows it:

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