ideal_lp.m、freqz_m.m、freqz_m2.m

function hd=ideal_lp(wc,N) %点0到N-1之间的理想脉冲响应
%wc=截止频率（弧度）%N=理想滤波器的长度
tao=(N-1)/2;
n=[0:(N-1)];
m=n-tao+eps; %加一个小数以避免0作除数
hd=sin(wc*m)./(pi*m);

function [db,mag,pha,grd,w]=freqz_m(b,a)
   [H,w]=freqz(b,a,1000,'whole');
   H=(H(1:501));
   w=(w(1:501));
   mag=abs(H);
   db=20*log10((mag+eps)/max(mag));
   pha=angle(H);
   grd=grpdelay(b,a,w);

function [db,mag,pha,w]=freqz_m2(b,a)
   [H,w]=freqz(b,a,1000,'whole');
   H=(H(1:1:501));
   w=(w(1:1:501));
   mag=abs(H);
   db=20*log10((mag+eps)/max(mag));
   pha=angle(H);
   grd=grpdelay;