lsfcxlpi.m

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

function [aQI, lsfQ] = LSFCxLPI (LSFC, lsfQP, LSFpar)
% Inverse quantize the LSF's, interpolate the quantized
% LSF's, convert to quantized LP parameters. If LSFC is
% empty, this is a packet loss frame.

% $Id: LSFCxLPI.m 1.1 2004/07/09 G.723.1-v2r1a $

% Inverse quantization of the LSFs
if (isempty (LSFC))
  LSFMode = 2;    % PLC frame
  NSplit = length (LSFpar.VQ);
  LSFC = zeros (NSplit, 1);
else
  LSFMode = 1;
end
lsfQ = IQLSF (LSFC, lsfQP, LSFMode, LSFpar);

% Interpolation of the LSF's and convert to LP
aQI = LSFxLPI (lsfQ, lsfQP, LSFpar);

return

%--------------------
function lsfQ = IQLSF (LSFC, lsfQP, LSFMode, LSFpar)
% LSFC is a vector of codebook codes

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

Nsplit = length (LSFpar.VQ);
i1 = 1;
for (k = 1:Nsplit)
  i2 = i1 + size (LSFpar.VQ{k}, 1) - 1;
  DlsfQ(i1:i2,1) = LSFpar.VQ{k}(:,LSFC(k) + 1);
  i1 = i2 + 1;
end

% Fix closely spaced LSF's
lsfQ = FixLSF (DlsfQ + Pval + LSFpar.Mean, LSFMode, LSFpar.Fix);
if (isempty (lsfQ))
  lsfQ = lsfQP;
end

return

%------------------------
function lsf = FixLSF (lsf, LSFMode, Fix)
% Fix closely spaced LSF's

Np = length (lsf);

lsf(1)  = max (lsf(1), Fix.Min);
lsf(Np) = min (lsf(Np), Fix.Max);

dwMin = Fix.MinSep(LSFMode);
dwTest = Fix.SepCheck(LSFMode);

NFix = 0;
for (m = 1:Fix.NIter)

  % Force a minimum separation
  for (j = 1:Np-1)
    dw = lsf(j+1) - lsf(j);
    if (dw < dwMin)
      lsf(j)   = lsf(j)   - 0.5 * (dwMin - dw);
      lsf(j+1) = lsf(j+1) + 0.5 * (dwMin - dw);
      NFix = NFix + 1;
    end
  end

  % Test separation (dwTest is a bit smaller than dwMin)
  dw = diff (lsf);
  TooClose = any (dw < dwTest);
  if (~ TooClose)
    break;	% No more fixes necessary
  end

end

if (NFix > 0)
  disp ('FixLSF: Fix for close LSFs');
end

if (TooClose)
  lsf = [];
  disp ('FixLSF: Fix not successful');
end

return