pitch_syn.m

the implement of the encoder and the decoder of the CELP

function [e0,buf]=pitch_syn(e0,buf,index,pgain)

global szsubf pdlyindx sub_cnt del_intv pcode TRUE FALSE

% Decode pitch code obtained from delta search into real index pointing to pitch delay table
if rem(sub_cnt-1,del_intv)~=0
    anch=del_intv*fix((sub_cnt-1)/del_intv)+1;
    index=pcode(anch);
    for i=1:rem(sub_cnt-1,del_intv)
        index=index+pcode(anch+i);
    end
end

leng=length(buf);
lb=leng-szsubf;

m=fix(pdlyindx(index));
buf(1:lb)=buf((1+szsubf):(lb+szsubf));

% For lags shorter than frame size(60), expand the adaptive codeword 
% the full codeword length by overlapping and adding the convolution
if pdlyindx(index)-m<10e-4                          % if integer pitch synthesis
    if(leng-m)>=lb+1
        if m<30                                     % Add in 3rd convolution
            buf((lb+1):(lb+m))=buf((lb-m+1):lb);
            buf((lb+m+1):(lb+m+m))=buf((lb+1):(lb+m));
            buf((lb+m+m+1):leng)=buf((lb+m+1):leng-m);
        else                                        % Add in 2dn convolution
            buf((lb+1):(lb+m))=buf((lb-m+1):lb);
            buf((lb+m+1):leng)=buf((lb+1):leng-m);
        end
    else
        buf((lb+1):leng)=buf((lb+1-m):leng-m);
    end
else    % else it's fractional pitch synthesis
    % Generate fractional pitch delay by interpolation
    [buf,buf1]=interpolate(buf,lb+1,szsubf,pdlyindx(index)-m,m);
    buf((lb+1):(leng))=buf1(1:szsubf);   
end

% Synthesize pitch
e0(1:szsubf)=e0(1:szsubf)+(pgain*buf(lb+1:lb+szsubf));
buf(lb+1:lb+szsubf)=e0(1:szsubf);