Problem when graphing digital filter chebyshev

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SGM SGM
SGM SGM 2021-8-29
评论： Paul 2021-9-1
Hello, I need to design a chebyshev digital filter, with cutoff frequencies of 250 and 2000 Hz, it should cut at 0.7 at these two frequencies. The code I am using does not meet the objectives, it is the following:
Fs = 44000;
Fn = Fs/2;
n = 3; Rp = 0.5;
Wn = [250 2000]/Fn;
[b a]=cheby1(n,Rp,Wn,'bandpass')
[h,w]=freqz(b,a)
plot(w,abs(h))
What I need to graph is what is shown in the image. The order is 3 and the ripple is 0.5

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回答（1 个）

Paul
Paul 2021-8-29
Ran in:
Need some some addition arguments to freqz(). Check its doc page for more information:
Fs = 44000;
Fn = Fs/2;
n = 3; Rp = 0.5;
Wn = [250 2000]/Fn;
[b a]=cheby1(n,Rp,Wn,'bandpass');
[h,f]=freqz(b,a,1024,Fs);
semilogx(f,abs(h))
Adjust n and Rp for the desired result.
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Juan Chehin
Juan Chehin 2021-9-1
Yes, but with some modifications
Fs=4400;
Fn = Fs/2;
n = 6;Rp = 0.5;
[b,a]=cheby1(n,Rp,[250/Fn,2000/Fn]);
[h,f]=freqz(b,a,1024,Fs);
plot(f,abs(h));
xlabel('Frequency (Hz)')
Paul
Paul 2021-9-1
Do you now have the desired result or is there still an open question? Did you intentionally reduce Fs from 44000 to 4400?

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