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I'm trying to make a frequency response of that function:

function

in matlab a made this:

d=[1 -0.494 0.6404];
p=[1 1.58567330897 0.96];
[h,w] = freqz(p,d,40000);
z = abs(h);
plot(w/pi,z);

d and p i calculated. The plot gives me this: plot

but in book has that answer: answer

as you can see the peak of magnitude is 2 and not about 6.5. '-' What am I doing wrong? H2 has an abs 1 because it is a all pass filter.

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Your answer is correct. Please note that your graph is in the range $0$ to $1$ while the graph in the text is in the output range of $-\pi$ to $+\pi$

There is some output scaling issue. But since you are getting the same curve, you are just messing some constants is all.

please try $\text{plot}(w,z)$

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Thanks for the answer. I thought that w/pi was for normalize like in ex 1 from freqz function documentation. I did what you said and i get this: enter image description here

sorry about my english i'm from brazil.

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