function [y,e]=voc(x, Aanal, Asyn, lseg);
% Syntax [y,e]=voc(x, Aanal, Asyn, lseg);
%
% very simple LPC vocoder to analyze the effects of spectral quantization.
% x - signal to analyze/synthesize - row vector !
% Aanal - LPC coeffs. for analysis (one vector per column (including a0=1))
% Asyn  - LPC for synthesis (same format)
% lseg  - length of segment. This function cannot handle overlapping
% y     - synthesized signal
% e     - error signal

[P, trames] = size(Aanal); P=P-1;
[Ps, tramess]= size(Asyn); Ps=Ps-1;
if (Ps ~= P | tramess ~= trames)
  error ('bad dimensions of parameter matrices');
end

%%%%%%%%%%%%%%%%% analysis %%%%%%%%%%%%%%%%%%%%%%%%%%%
% filtering to get excit - use initial and final conditions of the function
%  filter

init=zeros(1,P);	% initial conditions of the filter
e=[];			% excitation

pos=1;
for i=1:trames, 
 fen=x(pos:pos+lseg-1);
 pos=pos+lseg;		% window

 a=Aanal(:,i);		% filter
 [esmall,final]=filter(a,1,fen,init);	% filtering with initial cond.
 init=final;			% next init must be this final
 
 e=[e esmall];		% appending to the exct.
% plot(esmall);
% pause;
end

len=trames*lseg;
% figure(1); plot(1:len, x(1:len), 1:len, e);

%%%%%%%%%%%%%%%%%%% synthesis %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
init=zeros(1,P);	% initial conditions of the filter
y=[];			% excitation

pos=1;
for i=1:trames, 
 fen=e(pos:pos+lseg-1);
 pos=pos+lseg;		% window

 b=Asyn(:,i);		
 
 [ysmall, final]=filter(1,b,fen,init);	% filtering with initial cond.
 init=final;
 
 y=[y ysmall];		% appending to the synt. sig.
% plot(1:lseg, ysmall, 1:lseg, x(pos-lseg:pos-1) );
% pause;
end