function [pitch, ratio, cps]=pitch_cps(x, sammin, sammax, thr)
% Syntax: [pitch, ratio, cps]=pitch_cps(x, sammin, sammax, thr)
%     or: [pitch, ratio, cps]=pitch_cps(x)
%
% Pitch determination using cepstral method.
% x - frames of signal.
% sammin - minimal pitch period in samples - default 20
% sammax - maximal pitch period in samples - default 160
% thr - threshold for voiced/unvoiced determination - default ...
% pitch - pitch period, or 0, if unvoiced
% ratio - between c(max) and c(0)
% cps - complete cpestral vector
%
% the cepstrum is calculated as c=ifft(log(abs(fft(x)).^2)).
% The peak is then detected in the region of interest. The frame is declared
% voiced, if that peak reaches at least thr*c(0). Its position determinates
% the pitch. The length of fft is chosen to be at least 2*sammax.
 
if nargin==1,
  sammin=20;
  sammax=160;
  thr = 0.5;    % ?????
else 
  if (nargin ~= 4)
    error ('Bad no. of arguments');
  end
end
      
[r,c]=size(x);
if r>c,
  x=x';
end 

lx=length(x);  
if lx <= sammax
  disp ('for lx<=sammax, the results will not be very good...');
end  

ptsfft = 2^ceil(log2(sammax*2));

x=[x zeros(1,ptsfft-lx)];
lx=length(x);

c=abs(ifft(log(abs(fft(x)).^2)));
cps=c;					% output

c0=c(1);
c(1:sammin)=zeros(1,sammin);
c(sammax+2:lx)=zeros(1,lx-sammax-1);
[maxc,ind]=max(c);

ratio = maxc / c0;
if ratio > thr,
  pitch=ind-1;
else
  pitch=0;
end