void sf_zresp(real output[])
{
  int k,j;

  for(j=LPC-1; j>=0; j--)
      statelpc[j+IDIM] = statelpc[j];
  for (k=0; k<IDIM; k++) {
      real out = 0.0, sj, aj;
      sj = statelpc[LPC+IDIM-k-1];
      aj = sf_coeff[LPC];
      for (j=LPC-2; j>=1; j--) {
          out -= sj*aj;
          sj = statelpc[IDIM-k+j];
          aj = sf_coeff[j+1];
      }
      output[k] = out - sj*aj-statelpc[IDIM-k] * sf_coeff[1];
      statelpc[IDIM-1-k] = output[k];
  }
return;
}