www.pudn.com > voicebox2.zip > LPCAR2AM.M

function [am,em]=lpcar2am(ar,p); 
%LPCRR2AM Convert ar coefs to ar coef matrix [AM,EM]=(AR,P) 
%AM is a 3-dimensional matrix of size (p+1,p+1,nf) where p is the lpc order 
%and nf the number of frames. 
%The matrix AM(:,:,*) is upper triangular with 1's on the main diagonal 
%and contains the lpc coefficients for all orders from p down to 0. 
% 
%For lpc order p+1-r, AM(r,r:p+1,*), AM(p+1:-1:r,p+1,*) and EM(*,r) contain 
%the lpc coefficients, reflection coefficients and the residual energy respectively. 
%EM(:,1) is always 1. 
% 
%If A=am(:,:,*), R=toeplitz(rr(*,:)) and E=diag(em(*,:)), then 
% A*R*A'=E; inv(R)=A'*(1/E)*A; A*R is lower triangular with the same diagonal as E 
% 
% For each j in 1:P we have AM(j:end:-1:j+1,*) = AM(j:end-1,end,*)'*am(j+1:end,j+1:end,*) 
% 
% Also em(*,1:end)' = em(*,2:end)'.*(1-am(1:end-1,end,*).^2) 
 
 
%      Copyright (C) Mike Brookes 1997 
% 
%      Last modified Fri Sep 15 13:27:44 2000 
% 
%   VOICEBOX is a MATLAB toolbox for speech processing. Home page is at 
%   http://www.ee.ic.ac.uk/hp/staff/dmb/voicebox/voicebox.html 
% 
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
%   This program is free software; you can redistribute it and/or modify 
%   it under the terms of the GNU General Public License as published by 
%   the Free Software Foundation; either version 2 of the License, or 
%   (at your option) any later version. 
% 
%   This program is distributed in the hope that it will be useful, 
%   but WITHOUT ANY WARRANTY; without even the implied warranty of 
%   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the 
%   GNU General Public License for more details. 
% 
%   You can obtain a copy of the GNU General Public License from 
%   ftp://prep.ai.mit.edu/pub/gnu/COPYING-2.0 or by writing to 
%   Free Software Foundation, Inc.,675 Mass Ave, Cambridge, MA 02139, USA. 
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
 
[nf,p1] = size(ar); 
if any(ar(:,1)~=1) 
  ar=ar./ar(:,ones(1,p1)); 
end 
p0=p1-1; 
if nargin < 2 
   p=p0; 
end 
am=zeros(nf,p+1,p+1); 
em=ones(nf,p+1); 
e=ones(nf,1); 
rf=ar; 
if p>=p0 
   for jj=1:p+1-p0 
      am(:,jj:jj+p0,jj)=ar; 
   end 
else 
   for j=p0:-1:p+2 
      k = rf(:,j+1); 
      d = (1-k.^2).^(-1); 
      e = e.*d; 
      wj=ones(1,j-1); 
      rf(:,2:j) = (rf(:,2:j)-k(:,wj).*rf(:,j:-1:2)).*d(:,wj); 
   end 
   jj=0; 
end 
for jj=jj+1:p   
   j = p+2-jj; 
   k = rf(:,j+1); 
   d = (1-k.^2).^(-1); 
   e = e.*d; 
   wj=ones(1,j-1); 
   rf(:,2:j) = (rf(:,2:j)-k(:,wj).*rf(:,j:-1:2)).*d(:,wj); 
   am(:,jj:end,jj)=rf(:,1:j); 
   em(:,jj)=e; 
end 
em(:,end)=e./(1-rf(:,2).^2); 
am(:,end,end)=1; 
am=permute(am,[3 2 1]);