3、,并进行对比、分析和讨论。7T(2)对以下周期序列进行谱分析:%4⑻=cos—n7rnxs(ji)=cos—n+cos—n48选择FFT的变换区间N为8和16两种情况分别对以上序列进行频谱分析。分别打印其频谱特性曲线,并进行对比、分析和讨论。(3)对模拟周期信号进行谱分析:x8(t)=cos87rt+cosl6nt+cos20nt选择采样频率=64Hz,对变换区问N=16,32,64三种情况进行谱分析。分别打印其频谱特性曲线,并进行对比、分析和讨论。4、程序清单ifn<=3clc;x2(n+l)=n+l;clear;endL=8;if(n<=7)&(n>=4)N=4;x2(n+l)=8
4、-n;N1=L-N;endXl_0=ones(l,N);if(n7)Xl_l=zeros(l,Nl);x2(n+l)=0;X1=[X1_OXl_l]endn=l:L;endYl=fft(Xl,L);x2k_l=fft(x2,L);n=l:L;m=l:L;figure;figure;subplot(2,l,l);subplot{2,l,l);stem(n,Xl);%针状阁stem(m,x2);subplot(2,l,2);subplot(2,l,2);stem(n,abs(Yl));stem(m,abs(x2k_l));L=16;forn=0:L-lN=4;ifn<=3N1
5、=L-N;x3(n+l)=4-n;Xl_0=ones(l,N);endXl_l=zeros(l,Nl);if(n<=7)&(n>=4)X1=[X1_OXl_l];x3(n+l)=n-3;n=l:L;endYl=fft(Xl,L);if(n7)n=l:L;x3(n+l)=0;figure;endsubplot(2,l,l);endstem(n,Xl);x3k_l=fft(x3,L);subplot(2,l,2);m=l:L;stem(n,abs(Yl));figure;subplot(2,l,l);forn=0:L-lstem(m,x3);subplot(2,l,2);st
6、em(m,abs(x3k_l));L=256;n=O:l:L-l;x4=cos(n*pi/4);y4=fft(x4,L);figure;subplot(2/l/l);plot(n,x4);subplot(2,l,2);plot(n,abs(y4));L=256;n=O:l:L-l;x5=cos(n*pi/4)+cos(n*pi/8);y5=fft(x5,L);figure;subplot(2,l/l);plot(n,x5);subplot(2,l,2);plot(n,abs(y5));L=100;m=40;n=O:L-l;t=0:1/64:(m-1/64);%离散化x6=cos(8*p
7、i*t)+cos(16*pi*t)+cos(20*pi*t);y6=fft(x6,L);figure;subplot(2,l,l);plot(t,x6);subplot(2,l,2);plot(n,abs(y6));仿真波形(1)%i(n)=/?4(n)Q806卜Q40.201181614120QG>QQ236568fn+10