www.pudn.com > voicebox2.zip > LPCRA2PP.M

function pp=lpcra2pp(ra) 
%LPCAR2PP LPC: Convert ar filter autocorrelation to power spectrum polynomial in cos(w) PP=(RA) 
% pp is a polynomial such that |polyval(ra,e^jw)| = polyval(pp,cos(w)) 
 
%      Copyright (C) Mike Brookes 1998 
% 
%      Last modified Wed Jan 30 09:44:14 2002 
% 
%   VOICEBOX is a MATLAB toolbox for speech processing. Home page is at 
%   http://www.ee.ic.ac.uk/hp/staff/dmb/voicebox/voicebox.html 
% 
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persistent tp; 
[nf,p1]=size(ra); 
% we check here if p is the same as before and reuse the tp matrix 
if size(tp,1)~=p1 
   p=p1-1; 
   % chebyshev polynomials up to order p 
   tp=zeros(p1,p1); 
   tp(1,p1)=2; 
   tp(2,p)=2; 
   for i=3:p1 
      tp(i,p+2-i:p)=2*tp(i-1,p+3-i:p1)-tp(i-2,p+2-i:p); 
      tp(i,p1)=-tp(i-2,p1); 
   end 
   tp(1,p1)=1; 
end 
pp=ra*tp;