數(shù)字信號處理DFTMATLAB程序

1.實驗?zāi)康?.思考題clc;clear;N=128;A=dftmtx(N)Ai=conj(dftmtx(N));n=0:(N-1);k=0:(N-1);nk=n'*k;Wn=(sin(pi/8)+sin(pi/4)).^nkWk=conj(Wn)/N;求128點的DFT(分別用FFT函數(shù)和dftmtx函數(shù))clc;clear;N=128;n=0:N-1;x=sin(pi/8*n)+sin(pi/4*n);subplot(3,1,1)plot(n,x);gridontitle('原圖')y1=fft(x,N);A=dftmtx(N);y2=x(1:N)*A;subplot(3,1,2)plot(n,y1)gridontitle('FFT')subplot(3,1,3)plot(n,y2)gridontitle('dftmtx')原圖圖1求b)提高采樣點數(shù)值N=128,再求該信號的幅度頻譜，此時幅度頻譜發(fā)生了什clc;clear;N=40;n=0:N-1;t=0.01*nx=2*sin(4*pi*t)+5*sin(8*pi*t);subplot(2,1,1)plot(x(1:N))gridontitle('原圖')y1=fft(x,N);subplot(2,1,2)plot(n,y1(1:N))gridontitle('40點采樣')原圖5005050000505圖2clc;clear;N=128;n=0:N-1;t=0.01*nx=2*sin(4*pi*t)+5*sin(8*pi*t);subplot(2,1,1)plot(x(1:N))title('原圖')y1=fft(x,N);subplot(2,1,2)plot(n,y1(1:N))title('128點采樣')原圖50-1002040608010012014000000204060801001201400圖311對于128點采樣，f=128,T==，模擬頻率分別為=4,=8，那么，f1281211數(shù)字頻率分別為=T=4=,=T=8=。11128322212816(3)輸入為x(n)=2sin(n/4)u(n)，0n20N=20;n1=0:19;x=2*sin(n1*pi/4);X1=fft(x,N)n0:9;h=zeros(1,length(n2));h(1)=1;h(2)=2.5;h(3)=2.5;h(4)=1;X2=fft(h,N)y1=conv(x,h);vxhyNKXX時域卷積fftyNX0X02046810121416182020nX020n4681220n468N20;xsinnpi/4);fftxNhzeros(1,length(n2));h(2)=2.5;h(3)=2.5;ffthNftxhNNXKNcirconvXX0)KNcirconvXX頻域卷積X=fft(x.*h,N)5X0-100241618206024161820nXK=1/N*circonv(X1,X2,20)X50-1002468n1214161820圖5yx=fft(x,N);yr=fft(xr,N);yi=fft(i*xi,N);yryix1026x(nx10263210-10100200300400500600