lpfbfb.m

里面囊括了基于matlab滤波器设计的各种.m文件

 % [h0,h1,f0,f1] = lpfbfb(N,NP)
% lpfbfb --- The input integer N is the number of the independent 
coefficient
% of allpass filter. NP is the point number of the frequency response 
plot.
% This M-file will call the function M-file ap.m, which will design the 
allpass
% filter according to the input N. M=2*N-1 is the order of the allpass 
filter.
% So, M+1 is its length. The performance of the allpass filter will 
infulence
% the qualify of the lowpass filter H0. The reference of this program is
% "A New Class of Two-Channel Biorthogonal Filter Banks and Wavelet 
Bases" 
% IEEE TRANS. ON SIGNAL PROCESSING, VOL.43 NO.3,MARCH 1995

function [h0,h1,f0,f1] = lpfbfb(N,NP);
M = 2*N-1;
v = ap(M);
for I = 1:M+1
  h(2*I-1) = 0.5*v(I);
  h(2*I) = 0;
  v1(2*I-1) = v(I);
  v1(2*I) = 0; 
end
h(M+1) = 0.5;

for I = 1:2*M+1
 h0(I) = h(I);
 v2(I) = v1(I);
end

% v2 is v(exp(j*2*w))
h1 = conv(-v2,h0);
h1((max(size(h1))+1)/2) =h1((max(size(h1))+1)/2)+1;

% Synthesis Filter
for I = 1:max(size(h0))
 f1(I) = (-1)^(I-1)*h0(I);
end
for I = 1:max(size(h1))
 f0(I) = -(-1)^(I-1)*h1(I);
end

% draw the frequency response

H0 = freqz(h0,1,NP); H1 = freqz(h1,1,NP);
F0 = freqz(f0,1,NP); F1 = freqz(f1,1,NP);
x = 0.5/(NP-1)*(0:(NP-1));
plot(x,dbvalue(abs(H0)),'r');
hold on
plot(x,dbvalue(abs(F0)),'g');
plot(x,dbvalue(abs(H1)),'r')
plot(x,dbvalue(abs(F1)),'g');
title('Frequency Response of LPFBFB');
ylabel('Magnitude (dB)');
xlabel('Normalized Frequency');
hold off