[FFmpeg-devel] [PATCH] Common ACELP code & G.729 [2/7] - pitch lag decoding

[Michael Niedermayer]

On Sun, May 18, 2008 at 08:25:54AM +0700, Vladimir Voroshilov wrote:
> 2008/5/18 Michael Niedermayer <michaelni at gmx.at>:
> > On Wed, May 14, 2008 at 12:12:26AM +0700, Vladimir Voroshilov wrote:
> >> 2008/5/12 Michael Niedermayer <michaelni at gmx.at>:
> >> >
> >> > On Sun, May 11, 2008 at 09:42:26PM +0700, Vladimir Voroshilov wrote:
> >> >  > 2008/5/10 Michael Niedermayer <michaelni at gmx.at>:
> >>
[...]
> >> +void ff_acelp_update_past_gain_erasure(int16_t *quant_energy, int ma_pred_order)
> >> +{
> >> +    int avg_gain=quant_energy[ma_pred_order-1]; // (5.10)
> >> +    int i;
> >> +
> >> +    /* 4.4.3 of G.729, Equation 95 */
> >> +    for(i=ma_pred_order-1; i>0; i--)
> >> +    {
> >> +        avg_gain       += quant_energy[i-1];
> >> +        quant_energy[i] = quant_energy[i-1];
> >> +    }
> >> +#ifdef G729_BITEXACT
> >> +    if(ma_pred_order == 4)
> >> +    quant_energy[0] = FFMAX(avg_gain >> 2, -10240) - 4096; // -10 and -4 in (5.10)
> >> +    else
> >> +#endif
> >> +    quant_energy[0] = FFMAX(avg_gain / ma_pred_order, -10240) - 4096; // -10 and -4 in (5.10)
> >> +}
> >
> > Is this function used anywhere with a ma_pred_order != 4 ?
> 
> in fixed-point SIPR 16k (i still keeping it synced with common routines)
> with ma_pred_order == 2

quant_energy[0] = FFMAX(avg_gain >> log2_ma_pred_order, -10240) - 4096; // -10 and -4 in (5.10)

?


> 
> >> +void ff_acelp_update_past_gain(int16_t* quant_energy, int gain_corr_factor, int ma_pred_order)
> >> +{
> >> +    int i;
> >> +
> >> +    for(i=ma_pred_order-1; i>0; i--)
> >> +        quant_energy[i] = quant_energy[i-1];
> >> +
> >> +    /* 3.9.1 of G.729, Equation 72
> >> +      quant_energy[0] = 20*log10(gain_corr_factor) in (3.12)
> >> +      24660 = 10/log2(10) in (2.13) */
> >> +    quant_energy[0] = (24660 * av_clip_int16((ff_log2(gain_corr_factor) >> 2) - (13 << 13))) >> 15;
> >
> > (6165 * av_clip_int16((ff_log2(gain_corr_factor) >> 2) - (13 << 13))) >> 13;
> >
> > and i assume the av_clip_int16() is needed?
> 
> It can be removed if gain_corr_factor will be >=512
> This is not issue with G.729 since above condition is always true.
> But for G.729D gain_corr_factor can be even zero
> (while used log10(gain_corr_factor) formulas in spec shows that it should't)

hmm log(0) ...


> 
> Do you agree with adding above check in main loop for G.729D only and
> removing av_clip_int16 from the routine ?

If its needed iam fine with the check here or in the main loop.


> 
> >> +}
> >> +
> >> +int16_t ff_acelp_decode_gain_code(
> >> +    int gain_corr_factor,
> >> +    const int16_t* fc_v,
> >> +    int mr_energy,
> >> +    const int16_t* quant_energy,
> >> +    const int16_t* ma_prediction_coeff,
> >> +    int subframe_size,
> >> +    int ma_pred_order)
> >> +{
> >> +    int i;
> >> +    int energy;
> >> +    int exp;
> >> +
> >> +    /* 3.9.1 of G.729, Equation 66 */
> >> +    energy = sum_of_squares(fc_v, subframe_size, 0, 0);
> >> +
> >
> >> +    /* 24660 = 10/log2(10) in (2.13) */
> >> +    energy =  MULL(ff_log2(energy), -24660);
> >> +    /* mr_energy = Em + 10log(N) + 10log(2^26) */
> >> +    energy += mr_energy;
> >> +
> >> +    energy <<= 10; // (7.13) -> (7.23)
> >> +    /* 3.9.1 of G.729, Equation 69 */
> >> +    for(i=0; i<ma_pred_order; i++)
> >> +        energy += quant_energy[i] * ma_prediction_coeff[i];
> >> +
> >> +    /* 3.9.1 of G.729, Equation 71
> >> +      energy = 10^(energy / 20) = 2^(3.3219 * energy / 20) = 2^ (0.166 * energy)
> >> +      5439 = 0.166 in (0.15) */
> >> +    energy = (5439 * (energy >> 15)) >> 8; // (0.15) = (0.15) * (7.23)
> >
> > energy= mr_energy - (ff_log2(energy)<<10);
> 
> where is "energy =  MULL(ff_log2(energy), -24660);" ?

gone because *5439 undoes it
24660*5439 ~ 2^27


> this expression can't be evaluated with any constants/tables rescaling, imho.

scale ma_prediction_coeff[] and mr_energy by 2^C / 24660

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

There will always be a question for which you do not know the correct awnser.
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