Spectre (transformée de Fourier) d'un signal bruité

Spectrum (Fourier transform) of a signal with noise

Auteur/author : Christophe Dang Ngoc Chan (cdang)

Réalisé avec/made with Scilab

clear;clf;

// ******************
// variable ajustable

p=0.1; // pas

// ******************
// variables de base

x=[0:p:20*%pi]'; // x du sinus
N=size(x);
n=N(1,1); // nombre de points
s=1/p*(1:n); // fréquences

// nombres aleatoires, loi uniforme

y2=0.2*(rand(n,1)-0.5);

// ******************
// Calcul

y1=sin(x);
y3=y1+y2;
z1=abs(fft(y1))^2;
z2=abs(fft(y2))^2;
z3=abs(fft(y3))^2;

for i=1:n
  if z1(i)>500 then z1(i)=500; end
  if z3(i)>500 then z3(i)=500; end
end

// ******************
// affichage

subplot(3,2,1)
plot2d(x,y1,style=2,rect=[0,-1.1,60,1.1])
xtitle('signal sinusoïdal','Temps','Intensité')

subplot(3,2,2)
plot2d(s,z1,style=2,rect=[0,0,0.03,50])
xtitle('TF signal sinusoïdal','Fréq.','Puissance')

subplot(3,2,3)
plot2d(x,y2,style=2,rect=[0,-1.1,60,1.1])
xtitle('bruit','Temps','Intensité')

subplot(3,2,4)
plot2d(s,z2,style=2,rect=[0,0,0.03,50])
xtitle('TF bruit','Fréq.','Puissance')

subplot(3,2,5)
plot2d(x,y3,style=2,rect=[0,-1.1,60,1.1])
xtitle('signal sinusoïdal bruité','Temps','Intensité')

subplot(3,2,6)
plot2d(s,z3,style=2,rect=[0,0,0.03,50])
xtitle('TF signal sinusoïdal bruité','Fréq.','Puissance')

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