Function decorrelation

libavcodec/aacps.c:645–754

}

static void decorrelation(PSContext *ps, float (*out)[32][2], const float (*s)[32][2], int is34)
{
    float power[34][PS_QMF_TIME_SLOTS] = {{0}};
    float transient_gain[34][PS_QMF_TIME_SLOTS];
    float *peak_decay_nrg = ps->peak_decay_nrg;
    float *power_smooth = ps->power_smooth;
    float *peak_decay_diff_smooth = ps->peak_decay_diff_smooth;
    float (*delay)[PS_QMF_TIME_SLOTS + PS_MAX_DELAY][2] = ps->delay;
    float (*ap_delay)[PS_AP_LINKS][PS_QMF_TIME_SLOTS + PS_MAX_AP_DELAY][2] = ps->ap_delay;
    const int8_t *k_to_i = is34 ? k_to_i_34 : k_to_i_20;
    const float peak_decay_factor = 0.76592833836465f;
    const float transient_impact  = 1.5f;
    const float a_smooth          = 0.25f; //< Smoothing coefficient
    int i, k, m, n;
    int n0 = 0, nL = 32;
    static const int link_delay[] = { 3, 4, 5 };
    static const float a[] = { 0.65143905753106f,
                               0.56471812200776f,
                               0.48954165955695f };

    if (is34 != ps->is34bands_old) {
        memset(ps->peak_decay_nrg,         0, sizeof(ps->peak_decay_nrg));
        memset(ps->power_smooth,           0, sizeof(ps->power_smooth));
        memset(ps->peak_decay_diff_smooth, 0, sizeof(ps->peak_decay_diff_smooth));
        memset(ps->delay,                  0, sizeof(ps->delay));
        memset(ps->ap_delay,               0, sizeof(ps->ap_delay));
    }

    for (n = n0; n < nL; n++) {
        for (k = 0; k < NR_BANDS[is34]; k++) {
            int i = k_to_i[k];
            power[i][n] += s[k][n][0] * s[k][n][0] + s[k][n][1] * s[k][n][1];
        }
    }

    //Transient detection
    for (i = 0; i < NR_PAR_BANDS[is34]; i++) {
        for (n = n0; n < nL; n++) {
            float decayed_peak = peak_decay_factor * peak_decay_nrg[i];
            float denom;
            peak_decay_nrg[i] = FFMAX(decayed_peak, power[i][n]);
            power_smooth[i] += a_smooth * (power[i][n] - power_smooth[i]);
            peak_decay_diff_smooth[i] += a_smooth * (peak_decay_nrg[i] - power[i][n] - peak_decay_diff_smooth[i]);
            denom = transient_impact * peak_decay_diff_smooth[i];
            transient_gain[i][n]   = (denom > power_smooth[i]) ?
                                         power_smooth[i] / denom : 1.0f;
        }
    }

    //Decorrelation and transient reduction
    //                         PS_AP_LINKS - 1
    //                               -----
    //                                | |  Q_fract_allpass[k][m]*z^-link_delay[m] - a[m]*g_decay_slope[k]
    //H[k][z] = z^-2 * phi_fract[k] * | | ----------------------------------------------------------------
    //                                | | 1 - a[m]*g_decay_slope[k]*Q_fract_allpass[k][m]*z^-link_delay[m]
    //                               m = 0
    //d[k][z] (out) = transient_gain_mapped[k][z] * H[k][z] * s[k][z]
    for (k = 0; k < NR_ALLPASS_BANDS[is34]; k++) {