用FFT对信号作频谱分析的程序

实验（1）functionshiyan1x1=[1,1,1,1];n1=0:3;n2=4:7;xa=n1+1;xb=8-n2;x2=[xa,xb];xa1=4-n1;xb1=n2-3;x3=[xa1,xb1];X18=fft(x1,8);k1=0:8-1;subplot(3,2,1);stem(k1,abs(X18),'.');axis([0,8,0,1.2*max(abs(X18))]);title('8点DFT[x1]');ylabel('幅度');X116=fft(x1,16);k2=0:16-1;subplot(3,2,2);stem(k2,abs(X116),'.');axis([0,16,0,1.2*max(abs(X116))]);title('16点DFT[x1]');ylabel('幅度');X28=fft(x2,8);subplot(3,2,3);stem(k1,abs(X28),'.');axis([0,8,0,1.2*max(abs(X28))]);title('8点DFT[x2]');ylabel('幅度');X216=fft(x2,16);subplot(3,2,4);stem(k2,abs(X216),'.');axis([0,16,0,1.2*max(abs(X216))]);title('16点DFT[x2]');ylabel('幅度');X38=fft(x3,8);subplot(3,2,5);stem(k1,abs(X38),'.');axis([0,8,0,1.2*max(abs(X38))]);title('8点DFT[x3]');ylabel('幅度');X316=fft(x3,16);subplot(3,2,6);stem(k2,abs(X316),'.');axis([0,16,0,1.2*max(abs(X316))]);title('16点DFT[x3]');ylabel('幅度');实验（2）functionshiyan2n1=0:8-1;n2=0:16-1;x48=cos(pi/4*n1);x58=cos(pi/4*n1)+cos(pi/8*n1);x416=cos(pi/4*n2);x516=cos(pi/4*n2)+cos(pi/8*n2);X48=fft(x48,8);X416=fft(x416,16);X58=fft(x58,8);X516=fft(x516,16);k1=0:8-1;k2=0:16-1;subplot(2,2,1);stem(k1,abs(X48),'.');axis([0,8,0,5]);title('8点DFT[x4]');ylabel('幅度');subplot(2,2,2);stem(k2,abs(X416),'.');axis([0,16,0,10]);title('16点DFT[x4]');ylabel('幅度');subplot(2,2,3);stem(k1,abs(X58),'.');axis([0,8,0,10]);title('8点DFT[x5]');ylabel('幅度');subplot(2,2,4);stem(k2,abs(X516),'.');axis([0,16,0,10]);title('16点DFT[x5]');ylabel('幅度');实验（3）functionshiyan3Fs=64;T=1/Fs;N1=16;N2=32;N3=64;n1=0:N1-1;n2=0:N2-1;n3=0:N3-1;x816=cos(8*pi*n1*T)+cos(16*pi*n1*T)+cos(20*pi*n1*T);x832=cos(8*pi*n2*T)+cos(16*pi*n2*T)+cos(20*pi*n2*T);x864=cos(8*pi*n3*T)+cos(16*pi*n3*T)+cos(20*pi*n3*T);X816=fft(x816,16);X816=fftshift(X816);X832=fft(x832,32);X832=fftshift(X832);X864=fft(x864,64);X864=fftshift(X864);Tp=N1*T;F=1/Tp;k=-N1/2:N1/2-1;fk=k*F;subplot(3,1,1);stem(fk,abs(X816),'.');title('16点DFTx8');xlabel('f(Hz)');ylabel('幅度');Tp=N2*T;F=1/Tp;k=-N2/2:N2/2-1;fk=k*F;subplot(3,1,2);stem(fk,abs(X832),'.');title('32点DFTX8');xlabel('f(Hz)');ylabel('幅度');Tp=N3*T;F=1/Tp;k=