pitchol.m

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

function [L, xp] = PitchOL (x, LSubframe, PitchOLpar)
% Find the open loop pitch lag

% $Id: PitchOL.m 1.1 2003/11/21 G.723.1-v2r1a $

% Form the extended vector
xe = [PitchOLpar.xp; x];

% Form open-loop estimates
NSubframe = length (LSubframe);
LMem = length (PitchOLpar.xp);

j = LMem;
for (i = 1:NSubframe)
  Nx = LSubframe(i);
  L(i) = PitchEst (xe, j, Nx, PitchOLpar);
  j = j + Nx;
end

% Memory for next frame
xp = xe(end-LMem+1:end);

return

%---------------------
function Lo = PitchEst (x, iref, N, PitchOLpar)

PMin = PitchOLpar.PMin;
PMax = PitchOLpar.PMax;
PMultThr = PitchOLpar.PMultThr;

ELo = 1;
CLo = 0;
Lo = PMin;

L = PMin - 1;
i1 = iref - L;
i2 = i1 + N - 1;
EL = x(i1+1:i2+1)' * x(i1+1:i2+1);	% Energy for pitch lag PMin-1

for (L = PMin:PMax)
  i1 = i1 - 1;
  i2 = i2 - 1;

  % Recursive calculation of the energy term
  EL = EL + (x(i1+1)^2 - x(i2+2)^2);

  % Cross correlation term
  CL = x(i1+1:i2+1)' * x(iref+1:iref+N);

  % The error for a pitch predictor is
  %   e(n) = x(n) - p x(n-L)
  % The squared error for a frame is
  %   ES(L) = E(0) - 2p C(L) + p^2 E(L),
  % where E(L) = SUM x(n-L)^2 and C(L) = SUM x(n) x(n-L).
  % For a given L, the optimal coefficient p is
  %   popt = C(L) / E(L).
  % For this choice of p, the squared error is
  %  ES(L) = E(0) - C(L)^2 / E(L).
  % In the following code we find L which maximizes C(L)^2 / E(L). For
  % each L, we compare the largest values found so far (at Lo) with a
  % value at L and choose the new value of L if
  %  C(L)^2   C(Lo)^2
  %  ------ > -------  or C(L)^2 E(Lo) > C(Lo)^2 E(L)
  %   E(L)     E(Lo)
  % The search is conducted from small values of L up. Only positive values
  % of C(L) are candidates for a pitch lag. If the better value of squared
  % error is within Pmin of the Lo, it is kept. If it further away, the new
  % value must be at least 1/A times better.
  %  A C(L)^2 E(Lo) > C(Lo)^2 E(L)
  % This second check is used to avoid locking onto pitch multiples.
  if (EL > 0 & CL > 0)
    %  ( [ ------------------------- & --------------- ] | ...
    if ( ( (CL^2 * ELo > EL * CLo^2) & ((L-Lo) < PMin) ) | ...
           (PMultThr * CL^2 * ELo > EL * CLo^2) )
    %      ------------------------------------ )
      Lo = L;
      ELo = EL;
      CLo = CL;
    end
  end
end

return