shi31.m

matlab离散信号时域分析

%分析 sin(pi/4*k)+ cos(pi/8*k)的频谱在8点和16点上的dft
k=0:7;
k2=0:15;
n=8;
n2=16;
k3=8:15;
x3=cos(pi/4.*k)+sin(pi/8.*k);
x4=sin(pi/8.*k3);
x3=[x3 x4];
F_8=fft(x3,8);
F_16=fft(x3,16);
subplot(3,2,1);
stem(k/8,abs(F_8));
title('8点DFT');

subplot(3,2,2);
stem(k2/16,abs(F_16));


title('16 点DFT');

%用原理来的到的dft

%分析 sin(pi/4*k)和 cos(pi/8*k)  (长度分别为8 和16 )的频谱在8点和16点上的dft
k=0:7;
k2=0:15;
n=8;
n2=16;
x11=cos(pi.*k/4);

x22=sin(pi.*k2/8);
F_81=fft(x11);       % 8点的DFT
F_82=fft(x11,16);
F_161=fft(x22,8);
F_162=fft(x22);

yl=F_81+F_161;
yl2=F_82+F_162;
subplot(3,2,3);
stem(k/8,abs(yl));
title('原理8点DFT');

subplot(3,2,4);
stem(k2/16,abs(yl2));


title('原理 16 点DFT');


%%%%%%得到的结果一样 计算误差
subplot(3,2,5);
wc=abs(F_8-yl);
stem(k/8,abs(wc));
title(' 8 点DFT误差分析');
subplot(3,2,6);

wc2=abs(F_16-yl2);
stem(k2/16,abs(wc2));

title('16 点DFT误差分析');