q3.19.m

此matlab例程用于验证离散时间傅里叶变换的调制性质。

% Modulation Property of DTFT
clf;
w = -pi:2*pi/255:pi;              %w从-π到π
x1 = [1 2 3 4 5 6 7 8 9];     %一维数组x1分别赋值
x2 = [1 3 5 7 8 11 12 17 19];       %一维数组x2分别赋值
y = x1.*x2;                     %y数组的值是x1与x2相乘
h1 = freqz(x1, 1, w);            %h1=x1*e-jnw
h2 = freqz(x2, 1, w);             %h2=x2*e-jnw
h3 = freqz(y,1,w);               %h1=x1*e-jnw 
subplot(3,1,1)                    %h1的振幅谱
plot(w/pi,abs(h1));grid
xlabel('w/pi'); ylabel('h1振幅');   %X轴标记为w/π  Y轴标记为h1振幅
title('Magnitude Spectrum of First Sequence')
subplot(3,1,2)             %h2的振幅谱
plot(w/pi,abs(h2));grid
xlabel('w/pi'); ylabel('h2振幅');      %X轴标记为w/π  Y轴标记为h2振幅
title('Magnitude Spectrum of Second Sequence')
subplot(3,1,3)          %h2的振幅谱
plot(w/pi,abs(h3));grid
xlabel('w/pi'); ylabel('h3振幅');          %X轴标记为w/π  Y轴标记为h3振幅
title('Magnitude Spectrum of Product Sequence')