www.pudn.com > voicebox2.zip > LPCAR2FM.M

function [n,f,a,b]=lpcar2fm(ar,t) 
%LPCAR2RF Convert autoregressive coefficients to formant freq+amp+bw [N,F,A,B]=(AR,T) 
% 
% Input:   ar(:,p+1)  Autoregressive coefficients 
%          t          Threshold (see below) 
% Output:  n          Number of formants found 
%          f          Formant frequencies in normalized Hz (in increasing order) 
%          a          Formant amplitudes 
%          b          Formant bandwidths in normalized Hz 
% 
% The number of columns in the output arrays f, a and b is max(n); surplus positions 
% in any given row have f=b=0. 
% 
% In determining formants, poles are ignored if any of the following hold: 
%        (a) they are on the real axis 
%        (b) they have bandwidth > t*frequency (if t>0) 
%        (c) they have bandwidth > -t (if t<=0) 
 
%      Copyright (C) Mike Brookes 1997 
% 
%      Last modified Wed Jan  5 17:14:52 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); 
p=p1-1; 
d=(1:nf)'; 
zz=lpcar2zz(ar); 
ig=imag(zz)<=0; 
n=p1-1-sum(ig,2); 
mn=max(n); 
 
% remove redundant columns 
 
if mn
 1 
   if t>0 
      ig=ig | b>t*f; 
   else 
      ig=ig | b+t>0; 
   end 
end 
f(ig)=0; 
b(ig)=0; 
n=mn-sum(ig,2); 
m=max(n); 
 
% remove redundant columns 
 
[igf,ix]=sort(ig+f,2); 
dd=d(:,ones(1,m))+nf*(ix(:,1:m)-1); 
zz=reshape(zz(dd),nf,m); 
f=reshape(f(dd),nf,m); 
b=reshape(b(dd),nf,m); 
ig=reshape(ig(dd),nf,m); 
 
% now calculate gain 
ap=permute(ar,[1 3 2]); 
pw=permute(-2*pi*1i*(0:p),[1 3 2]); 
a=abs(sum(ap(:,ones(1,m),:).*exp(pw(ones(1,nf),ones(1,m),:).*f(:,:,ones(1,p1))),3)).^(-1);