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function [freq, Pyy, A] = lpcspectrum(frame, fs, lpcOrder, lpcmethod, fspace) 
% LPCSPECTRUM Short term LPC to get magnitude spectrum information 
%    Usage : [freq, Pyy, A] = lpcspectrum(frame, fs, lpcOrder, lpcmethod, fspace) 
%    frame means frame vector from some wavefile. 
%    fs means sample rate of the wavefile. 
%    lpcOrder means order of LPC coefficients. 
%    lpcmethod presents two different extraction rules. Its value is either 1 or 2. 
%    fspace means frequency spacing. 
%    freq represents frequency components 
%    Pyy represents log magnitudes corresponding to frequency components. 
%    A means LPC coefficients. 
% 
%    Cheng-Yuan Lin 2003, January, 22. 
 
if nargin<5,  
   fspace = 0: 10 : (fs/2);  %10 Hz spacing. 
end; 
if nargin<4, lpcmethod = 2; end; 
 
switch lpcmethod, 
case 1, 
   % general version 
   frameSize = length(frame); 
   [A, K, E] = ldlpc(frame, lpcOrder); 
   sequence = [A zeros(1, frameSize-lpcOrder-1)]; 
   half = ceil(frameSize/2); 
   Pyy  = 1./abs(fft(sequence)); 
   Pyy  = Pyy(1:half);  %fft spectrum is symmetric. 
   Pyy  = 20*log10(Pyy); 
   spectfactor = (fs/2)/length(Pyy); 
   freq = [1: spectfactor : (fs/2)]; 
case 2, 
   % Using MATLAB function : freqz. 
   A    = real(lpc(frame, lpcOrder)); 
   Pyy  = real(20*log10(freqz(1, A, fspace, fs)));  % LPC spectrum 
   freq = (fs/2)/length(Pyy)*(1:length(Pyy))'; 
end;