program_4_2.m

《数字信号处理：基于计算机的方法（第三版）》资源下载第三部分。 著者： （美）米特拉著 作译者： 孙洪等译 ISBN号： 7-121-02652-X 出版日期： 2006-06 出版

% Program 4_2
% Program to Design Butterworth Lowpass Filter
%
% Type in the filter order and passband edge frequency
N = input('Type in filter order = ');
Wn = input('3-dB cutoff angular frequency = ');
% Determine the transfer function
[num,den] = butter(N,Wn,'s');
%  Compute and plot the frequency response
omega = [0: 200: 12000*pi];
h = freqs(num,den,omega);
plot (omega/(2*pi),20*log10(abs(h)));
xlabel('Frequency, Hz'); ylabel('Gain, dB');