Function tilt_factor

libavcodec/wmavoice.c:540–548

* Get the tilt factor of a formant filter from its transfer function * @see #tilt_factor() in amrnbdec.c, which does essentially the same, * but somehow (??) it does a speech synthesis filter in the * middle, which is missing here * * @param lpcs LPC coefficients * @param n_lpcs Size of LPC buffer * @returns the tilt factor */

 * @returns the tilt factor
 */
static float tilt_factor(const float *lpcs, int n_lpcs)
{
    float rh0, rh1;

    rh0 = 1.0     + ff_dot_productf(lpcs,  lpcs,    n_lpcs);
    rh1 = lpcs[0] + ff_dot_productf(lpcs, &lpcs[1], n_lpcs - 1);

    return rh1 / rh0;
}

/**
 * Derive denoise filter coefficients (in real domain) from the LPCs.