clear all;clc;

% Filtre de Butterworth
N=6
wc=0.7032
[b1 a1]=butter(N,wc/pi);  
figure(1);
freqz(b1,a1)
axis([0 1 -20 0])

%Filtrage numérique:
t=0.001:0.001:1;
x=sin(2*pi*20*t)+cos(2*pi*500*t);
dataIn=x'+0.1*randn(1000,1);
dataOut=filter(b1,a1,dataIn);
figure(2);
subplot(2,1,1);plot(1:1000,dataIn);
legend('Signal bruité');grid;
subplot(2,1,2);plot(1:1000,dataOut,'r');
legend('Signal filtré');grid;

% Filtre de Chebyshev
N=4;
ep=0.50885;
wc=0.6283;
[b2,a2] = cheby1(N,ep,wc/pi);
figure(3);
freqz(b2,a2);
axis([0 1 -30 0])

%Filtrage numérique
t=0.001:0.001:1;
x=sin(2*pi*20*t)+cos(2*pi*500*t);
dataIn=x'+0.1*randn(1000,1);
dataOut=filter(b2,a2,dataIn);
figure(4);
subplot(2,1,1);plot(1:1000,dataIn);
legend('Signal bruité');grid;
subplot(2,1,2);plot(1:1000,dataOut,'r');
legend('Signal filtré');grid;

%Comparaison entre les deux filtres
figure(5);
freqz(b1,a1);
hold on;
freqz(b2,a2);axis([0 1 -20 0])
legend('Réponse de Butterworth','Réponse de Chebyshev');