Difference in the output of butterworth and chebyshev fitlers

Question

Stefan 2014-8-8

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/146814-difference-in-the-output-of-butterworth-and-chebyshev-fitlers

编辑： Stefan 2014-8-9

Hello,

I have used two filters for the atatched signal data 1)butterworth from here and 2)chebyshev using the below codes

clc;
clear all;
  %----------------butterworht filter------------------%
filtered1 = bandstop_butterworth(output2,[.2 .35],100,2);
finalsignal = bandstop_butterworth(filtered1,[.5 4],100,2);
    %--------------Freq spectrum----------------%
Fs=100;
T=1/Fs;
L=length(finalsignal);
t=(0:L-1)*T;
NFFT=2^nextpow2(L);
Y=fft(finalsignal,NFFT)/L;
f=Fs/2*linspace(0,1,NFFT/2+1);
figure(2),subplot(2,1,1),plot(f,2*abs(Y(1:NFFT/2+1)));hold on;
title('Output of butterworth filters');
xlabel('Frequency');
ylabel('amplitude');
%----------------chebyshev filter---------%
Fs=100;
Fn=Fs/2;
Ws1=[0.2 0.35]/Fn;
n1=2;
R=20;
[b1,a1]=cheby2(n1,R,Ws1,'stop');
[sos1,g1]=tf2sos(b1,a1);
Ws2=[0.5 4]/Fn;
n2=2;
[b2,a2]=cheby2(n2,R,Ws2,'stop');
[sos2,g2]=tf2sos(b2,a2);
YF1=filtfilt(sos1,g1,output2);
YF2=filtfilt(sos2,g2,YF1);
    %----------Freq spectrum------------------%
Fs=100;
T=1/Fs;
L=length(YF2);
t=(0:L-1)*T;
NFFT=2^nextpow2(L);
Y=fft(YF2,NFFT)/L;
f=Fs/2*linspace(0,1,NFFT/2+1);
figure(2),subplot(2,1,2),plot(f,2*abs(Y(1:NFFT/2+1)),'-r');
title('Output of chebyshev filters');
xlabel('Frequency');
ylabel('amplitude');
%--------------------------------------%
I wonder why the otuptu of fitlers has different frequenc spectrum(figure attached).
Can someone explain the reason behind the difference between the spectrum of two filters adn which is the best to use.
Thanks.