lpxlsfq.m

ITU-T G.723.1 Speech Coder: Matlab implementation This package implements the speech coder and de

function LSFC = LPxLSFQ (a, lsfQP, LSFpar)
% Convert LP parameters to LSFs, quantize the LSFs.

% $Id: LPxLSFQ.m 1.3 2004/07/05 G.723.1-v2r1a $

% Convert to LSFs
ap = a .* LSFpar.ECWin;
lsf = poly2lsf (ap);	% lsf's are in radians

% Quantize the LSFs
LSFC = QLSF (lsf, lsfQP, LSFpar);

return

%--------------------
function LSFC = QLSF (lsf, lsfQP, LSFpar)
% Quantize LSFs
% - Weighting inversely proportional to LSF spacings
% - Form the LSFs less the mean LSFs
% - Calculate the prediction error from the LSFs from the
%   previous frame

Np = length (lsf);

% Form the weight vector
% W(i) = 1 / min (lsf(i+1)-lsf(i),lsf(i)-lsf(i-1))
Slsf = diff (lsf);
W = 1 ./ min ([Slsf(1); Slsf], [Slsf; Slsf(end)]);

% Calculate the prediction error
Pval = LSFpar.Pcof * (lsfQP - LSFpar.Mean);
Dlsf = (lsf - LSFpar.Mean) - Pval;

IQ = SVQLSF (Dlsf, W, LSFpar.VQ);
LSFC = IQ - 1;

return

%--------------------
function IQ = SVQLSF (Dlsf, W, YQ)
% Returns a vector of codebook indices

Nsplit = length (YQ);

i1 = 1;
for (k = 1:Nsplit)
  i2 = i1 + size (YQ{k}, 1) - 1;
  IQ(k) = VQ (Dlsf(i1:i2), W(i1:i2), YQ{k});
  i1 = i2 + 1;
end

return

%--------------------
function Index = VQ (x, W, YQ)
% Returns the codebook index minimizing the weighted error

% We want to minimize (where W is a diagonal matrix)
%   (x-y)'W (x-y) = x'Wx - 2 y'W x + y'W y
%                 = x'Wx + y'W (y - 2 x)

Ny = size (YQ, 2);
ErrMin = inf;
for (k = 1:Ny)
  Err = (W .* YQ(:,k))' * (YQ(:,k) - 2 * x);
  if (Err < ErrMin)
    ErrMin = Err;
    Index = k;
  end
end

return