实验四 FFT信号的频谱分析实验Microsoft Word 文档

clearall;T1=1/1000;n=0:64/(1000*T1);A=444.128;a=50*sqrt(2.0);w0=50*sqrt(2.0)*pi;xn1=A*exp(-a*n*T1).*sin(w0*n*T1);Xk1=fft(xn1,1024);subplot(322);stem(n,xn1,'.');gridonxlabel('n');ylabel('x(n)');title('1000Hz采样x(n)');k=0:1023;wk=2*k/1024;subplot(321);plot(wk,abs(Xk1));gridon;xlabel('\omega/\pi');ylabel('|X(e^j^\omega)|');title('FT[x(n)]');%用300Hz采样频率T2=1/300;n2=0:64/(1000*T2);A=444.128;a=50*sqrt(2.0);w0=50*sqrt(2.0)*pi;xn2=A*exp(-a*n2*T2).*sin(w0*n2*T2);Xk2=fft(xn2,1024);subplot(324);stem(n2,xn2,'.');gridon;title('300Hz采样x(n2)');xlabel('n');ylabel('x(n2)');k=0:1023;wk=2*k/1024;subplot(323);plot(wk,abs(Xk2));gridon;title('(a)FT[x(n2)]');xlabel('\omega/\pi');ylabel('|X(e^j^\omega)|');%用200Hz采样频率T3=1/200;n3=0:64/(1000*T3);A=444.128;a=50*sqrt(2.0);w0=50*sqrt(2.0)*pi;xn3=A*exp(-a*n3*T3).*sin(w0*n3*T3);Xk3=fft(xn3,1024);subplot(326);stem(n3,xn3,'.');gridon;title('200Hz采样x(n3)');xlabel('n');ylabel('x(n3)');k=0:1023;wk=2*k/1024;subplot(325);plot(wk,abs(Xk3));gridon;title('(a)FT[x(n3)]');xlabel('\omega/\pi');ylabel('|X(e^j^\omega)|');%x2n和x3nM=8;xa=1:(M/2);xb=(M/2):-1:1;x2n=[xa,xb];%产生长度为8的三角波序列x2(n)x3n=[xb,xa];X2k8=fft(x2n,8);X2k16=fft(x2n,16);X3k8=fft(x3n,8);X3k16=fft(x3n,16);figure(2);N=8;f=2/N*(0:N-1);subplot(2,2,1);stem(f,abs(X2k8),'.');%绘制8点DFT的幅频特性图title('(2a)8点DFT[x_2(n)]');xlabel('ω/π');ylabel('幅度');subplot(2,2,3);stem(f,abs(X3k8),'.');%绘制8点DFT的幅频特性图title('(3a)8点DFT[x_3(n)]');xlabel('ω/π');ylabel('幅度');N=16;f=2/N*(0:N-1);subplot(2,2,2);stem(f,abs(X2k16),'.');%绘制8点DFT的幅频特性图title('(2a)16点DFT[x_2(n)]');xlabel('ω/π');ylabel('幅度');subplot(2,2,4);stem(f,abs(X3k16),'.');%绘制8点DFT的幅频特性图title('(3a)16点DFT[x_3(n)]');xlabel('ω/π');ylabel('幅度');%x4n和x5nN=8;n=0:N-1;x4n=cos(pi*n/4);x5n=cos(pi*n/4)+cos(pi*n/8);X4k8=fft(x4n,8);X4k16=fft(x4n,16);X5k8=fft(x5n,8);X5k16=fft(x5n,16);figure(3);N=8;f=2/N*(0:N-1);subplot(2,2,1);stem(f,abs(X4k8),'.');%绘制8点DFT的幅频特性图title('(4a)8点DFT[x_4(n)]');xlabel('ω/π');ylabel('幅度');subplot(2,2,3);stem(f,abs(X5k8),'.');%绘制8点DFT的幅频特性图title('(5a)8点DFT[x_5(n)]');xlabel('ω/π');ylabel('幅度');N=16;f=2/N*(0:N-1);subplot(2,2,2);stem(f,abs(X4k16),'.');%绘制8点DFT的幅频特性图title('(4a)16点DFT[x_4(n)]');xlabel('ω/π');ylab