信号与系统实验报告（川大版）

clear; h2=[-0.0238,0.0562,-0.0575,-0.1302,0.5252, -0.6842,-0.3129,5.6197,5.6197, -0.3129,-0.6842,0.5252,-0.1302,-0.0575,0.0562,-0.0238]; k1=0:15; n=-4:4; x1=cos(0.25*pi*n); y1=conv(h2,x1);%计算序列f1与f2的卷积和f k0=k1(1)+n(1); %计算序列f非零样值的起点位置 k3=length(x1)+length(h2)-2; %计算卷积和f的非零样值的宽度 k=k0:k0+k3; %确定卷积和f非零样值的序号向量 subplot(2,2,1); stem(k,y1); title('x1[n]与h2[n]的卷积和y1[n]'); xlabel('k'); ylabel('y1[k]'); x2=cos(1.25*pi*n); y2=conv(h2,x2); subplot(2,2,2); stem(k,y2); title('x2[n]与h2[n]的卷积和y2[n]'); xlabel('k'); ylabel('y2[k]'); x3=x1+x2; y3=conv(h2,x3); subplot(2,2,3); stem(k,y3); title('x3[n]与h2[n]的卷积和y3[n]'); xlabel('k'); ylabel('y3[k]'); 5

3.(a) fs=128; t=1/fs; L=256; n=0:1:L-1; x1=cos(0.25*pi*n); x2=cos(1.25*pi*n); x3=x2+x1; N = 2^nextpow2(L); X1=fft(x1,N)/N*2; X2=fft(x2,N)/N*2; X3=fft(x3,N)/N*2; f=fs/N*(0:1:N-1); figure; subplot(2,1,1); plot(f,abs(X1)); title('幅值频谱'); xlabel('频率(HZ)'); ylabel('幅值'); subplot(2,1,2); plot(f,angle(X1)); title('相位频谱'); xlabel('频率(HZ)'); ylabel('相位'); figure; subplot(2,1,1); plot(f,abs(X2)); title('幅值频谱'); xlabel('频率(HZ)'); ylabel('幅值'); subplot(2,1,2); plot(f,angle(X2)); title('相位频谱'); xlabel('频率(HZ)'); ylabel('相位'); figure; subplot(2,1,1); plot(f,abs(X3)); title('幅值频谱'); xlabel('频率(HZ)'); ylabel('幅值'); subplot(2,1,2); plot(f,angle(X3)); title('相位频谱'); 6

xlabel('频率(HZ)'); ylabel('相位'); 7

(b) fs=128; t=1/fs; L1=256; n=0:1:L1-1; h1=[0.0031,0.0044,-0.0031,-0.0272,-0.0346,0.0374,0.1921,0.3279,0.3279,0.1921,0.0374,-0.0346,-0.0272,-0.0031,0.0044,0.0031]; x1=cos(0.25*pi*n); x2=cos(1.25*pi*n); x3=x2+x1; N = 2^nextpow2(L1); X1=fft(x1,N)/N*2; X2=fft(x2,N)/N*2; X3=fft(x3,N)/N*2; H1=fft(h1,N)/N*2; Y11=fft(x1,N)/N.*2.*fft(h1,N)/N.*2; Y12=fft(x2,N)/N.*2.*fft(h1,N)/N.*2; Y13=fft(x3,N)/N.*2.*fft(h1,N)/N.*2; f=fs/N*(0:1:N-1); figure; subplot(2,1,1); plot(f,abs(H1)); title('幅值频谱'); xlabel('频率(HZ)'); ylabel('幅值'); subplot(2,1,2); plot(f,angle(H1)); title('相位频谱'); xlabel('频率(HZ)'); ylabel('相位'); figure; subplot(2,1,1); plot(f,abs(Y11)); title('幅值频谱'); xlabel('频率(HZ)'); ylabel('幅值'); subplot(2,1,2); plot(f,angle(Y11)); title('相位频谱'); xlabel('频率(HZ)'); ylabel('相位'); figure; subplot(2,1,1); plot(f,abs(Y12)); 8