// Input : n element envelope spectral curve
// Output: m lpc coefficients, excitation energy
float lpc_from_curve(float[] curve, float[] lpc)
{
int n = ln;
float[] work = new float[n + n];
float fscale = (float)(.5 / n);
int i, j;
// input is a real curve. make it complex-real
// This mixes phase, but the LPC generation doesn't care.
for (i = 0; i < n; i++)
{
work[i * 2] = curve[i] * fscale;
work[i * 2 + 1] = 0;
}
work[n * 2 - 1] = curve[n - 1] * fscale;
n *= 2;
fft.backward(work);
// The autocorrelation will not be circular. Shift, else we lose
// most of the power in the edges.
for (i = 0, j = n / 2; i < n / 2;)
{
float temp = work[i];
work[i++] = work[j];
work[j++] = temp;
}
return(lpc_from_data(work, lpc, n, m));
}
