%Creat a random unbalanced sigal
load mtlb;     %導入庫函數
x=mtlb;        %定義函數
figure(1)
subplot(311);
plot(0:4000,x);
xlabel('n');
ylabel('x(n)');
title('random unbalanced signal x');
%Create a Rectangular window
n0=0;
R=128;
n1=4000;
n2=n0+R;
n=[n0:n1];
w=[(n-n0)>=0];
wd=[(n-n2-1)<=0];
WN=w.*wd;
subplot(312);
stem(n,WN);
xlabel('n');
ylabel('W(N)');
title('Rectangular Window WN');
grid
%Block the signal with the window
x1=x';
y1=x1.*WN;
subplot(313);
plot(n,y1);
xlabel('n');
ylabel('y1');
title('The first block');
%
k=0:128;
y3=[y1(n0+1:n2+1)];
figure(4)
subplot(211);
plot(k,y3);
xlabel('k');
ylabel('y3');
title('The effective signal');
%
%Make the FFT
yn=fft(y3);%對短持續信號FFT
YN=abs(yn);%觀察其頻譜
plot(yn);