lsp_az.m

VAD G729 for mobile phone

function a=Lsp_Az(lsp)
%/*-------------------------------------------------------------*
% *  Procedure Lsp_Az:                                          *
% *            ~~~~~~                                           *
% *   Compute the LPC coefficients from lsp (order=10)          *
% *-------------------------------------------------------------*/
%  Word16 lsp[],    /* (i) Q15 : line spectral frequencies            */
%  Word16 a[]       /* (o) Q12 : predictor coefficients (order = 10)  */

%f1=zeros(1,6);%(-1,0,1,...,5)
%f1(1)=1;
%f1(2)=-2*lsp(1);
k=2;
pp=2;

f1=zeros(1,7);
f1(2)=1;
for i=1:5
    temp=f1;
    f1(i+2)=-2*lsp(2*i-1)*f1(i+1)+2*f1(i);
    for j=i-1:-1:1
        f1(j+2)=temp(j+2)-2*lsp(2*i-1)*temp(j+1)+temp(j);
    end
end
%round(f1*2^24)'



f2=zeros(1,7);
f2(2)=1;
for i=1:5
    temp=f2;
    f2(i+2)=-2*lsp(2*i)*f2(i+1)+2*f2(i);
    for j=i-1:-1:1
        f2(j+2)=temp(j+2)-2*lsp(2*i)*temp(j+1)+temp(j);
    end
end
%round(f2*2^24)'

for i=5:-1:1
    f1(i+2)=f1(i+2)+f1(i+1);
    f2(i+2)=f2(i+2)-f2(i+1);
end
%round(f2*2^24)'

a(1)=1;
for i=2:6
    a(i)=0.5*(f1(i+1)+f2(i+1));
end
for i=7:11
    a(i)=0.5*(f1(11-i+3)-f2(11-i+3));
end