n=0:63;
xb1=exp(-0.1*n).*sin(2*pi*0.0625*n);
w=randn(1,64);
y1=xb1+w;
xb2=exp(-0.1*n).*sin(2*pi*0.2375*n);
w=randn(1,64);
y2=xb2+w;
xb3=exp(-0.1*n).*sin(2*pi*0.4325*n);
w=randn(1,64);
y3=xb3+w;
xb4=exp(-0.1*n).*sin(2*pi*0.5625*n);
w=randn(1,64);
y4=xb4+w;
figure
subplot(4,1,1);stem(y1);title('信號圖形(f=0.0625)');
subplot(4,1,2);stem(y2);title('信號圖形(f=0.2375)');
subplot(4,1,3);stem(x3);title('信號圖形(f=0.4325)');
subplot(4,1,4);stem(x4);title('信號圖形(f=0.5625)');
figure
subplot(4,1,1);stem(abs(fft(y1,64)));title('y1的幅度譜(f=0.0625)');
subplot(4,1,2);stem(abs(fft(y2,64)));title('y2的幅度譜(f=0.2725)');
subplot(4,1,3);stem(abs(fft(y3,64)));title('y3的幅度譜(f=0.4325)');
subplot(4,1,4);stem(abs(fft(y4,64)));title('y4的幅度譜(f=0.5625)');