Using the following specifications:
Fs = 172800;Fc = 70000;
where "Fs" represents the sampling frequency and "Fc" represents the cutoff frequency, I created a digital filter in two different ways:
1. Using the BUTTER function.
[B ,A] = butter(4,Fc/(Fs/2));
2. Using the BILINEAR function to convert the analog filter designed using the BUTTER function into a digital filter through a bilinear transformation.
[Bs,As] = butter(4,Fc*2*pi,'s');[Bz,Az] = bilinear(Bs,As,Fs);
I then used the FVTOOL function to compute the magnitude response and compared the two results:
fvtool(B,A,Bz,Az);
Notice that the results of the two magnitude responses are not the same even though I am using the same specifications.
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