lpasflter.m

lowpass FIR filter 的MATLAB代码

clear all;
close all;
len=4096;
df=2*pi/len;
Wp=floor(0.26*pi/df);
Ws=floor(0.3*pi/df);
tr_width=Ws-Wp;
%M=ceil(6.6*pi/(df*tr_width))+1;   %抽头数
M=68;
win_ham=(hamming(M))'; %'
%ideal frequence response
sig(1:len)=0;
sig(1:Wp)=1;
sig(len-Wp+2:len)=1;
ht=ifft(sig,len);
TaplenDiv2=floor(M/2);
cht(1:TaplenDiv2)=ht(len-TaplenDiv2+1:len);   
cht(TaplenDiv2+1:M)=ht(1:TaplenDiv2);
w_cht=cht.*win_ham;         
plot(1:M,w_cht);
h_cht=abs(fft(w_cht,len));
m=(1:len);
Wpp=round(0.25*pi/df);
%Wpp=round((Wp+Ws)/2);
%Wpp=Wp;
vf=20*log10(h_cht(Wpp));
figure;
plot(m,20*log10(h_cht));
xlabel('*df KHZ');
title('频域响应');
grid on;
text(Wpp,vf,['\leftarrow','F(0.25pi)=',num2str(vf),'db']);