% AddWindowDFT


clear;
disp('用DFT對離散信號進行譜分析');
disp('通過選用不同的加窗函數來抑制信號截斷造成的頻譜泄漏');
Repeat = 1;

disp('輸入信號x(n),n為下標');
n = input('n=');
L = length(n);
x = input('x=');
    
disp(sprintf('輸入截取信號的長度N(即窗長),N<%d',L));
N = input('N=');
    
x1 = x(1:N);
k = 0:L-1;
Xk = dft(x,L);
Xk1 = dft(x1,L);
    
figure;
subplot(2,1,1),stem(n,x),title('原始信號');
subplot(2,1,2),stem(k,abs(Xk)),title('原始信號頻譜');
    
figure;
subplot(2,1,1),stem(n,[x1,zeros(1,L-N)]),title('不加窗的截斷信號');
subplot(2,1,2),stem(k,abs(Xk1)),title('不加窗的信號頻譜'); 
    
while Repeat == 1   
    disp('選擇窗函數');
    disp('1:boxcar');
    disp('2:triang');
    disp('3:hanning');
    disp('4:hamming');
    disp('5:blackman');
    Ans = input('Choose=');    
    
    switch Ans
        case 1
            w = (boxcar(N))';
            x2 = x1.*w;
            Xk2 = dft(x2,L);
            
            figure;
            subplot(2,1,1),stem(n,[x2,zeros(1,L-N)]),title('用boxcar截斷信號');
            subplot(2,1,2),stem(k,abs(Xk2)),title('加窗后的信號頻譜');
            
        case 2
            w = (triang(N))';
            x2 = x1.*w;
            Xk2 = dft(x2,L);
            
            figure;
            subplot(2,1,1),stem(n,[x2,zeros(1,L-N)]),title('用triang截斷信號');
            subplot(2,1,2),stem(k,abs(Xk2)),title('加窗后的信號頻譜');
            
        case 3
            w = (hanning(N))';
            x2 = x1.*w;
            Xk2 = dft(x2,L);
            
            figure;
            subplot(2,1,1),stem(n,[x2,zeros(1,L-N)]),title('用hanning截斷信號');
            subplot(2,1,2),stem(k,abs(Xk2)),title('加窗后的信號頻譜');
            
        case 4
            w = (hamming(N))';
            x2 = x1.*w;
            Xk2 = dft(x2,L);
            
            figure;
            subplot(2,1,1),stem(n,[x2,zeros(1,L-N)]),title('用hamming截斷信號');
            subplot(2,1,2),stem(k,abs(Xk2)),title('加窗后的信號頻譜');
            
        case 5
            w = (blackman(N))';
            x2 = x1.*w;
            Xk2 = dft(x2,L);
            
            figure;
            subplot(2,1,1),stem(n,[x2,zeros(1,L-N)]),title('用blackman截斷信號');
            subplot(2,1,2),stem(k,abs(Xk2)),title('加窗后的信號頻譜');
            %otherwise
            %disp('請選擇窗函數');
    end      
    Repeat = input('Still want to continue,Yes=1 No=0? Ans=');
end