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FFmpeg
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#include "libavutil/common.h"#include "libavutil/ffmath.h"#include "libavutil/float_dsp.h"#include "libavutil/mathematics.h"#include "avcodec.h"#include "acelp_pitch_delay.h"#include "celp_math.h"#include "audiodsp.h"Go to the source code of this file.
Functions | |
| void | ff_acelp_update_past_gain (int16_t *quant_energy, int gain_corr_factor, int log2_ma_pred_order, int erasure) |
| Update past quantized energies. More... | |
| int16_t | ff_acelp_decode_gain_code (AudioDSPContext *adsp, 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) |
| Decode the adaptive codebook gain and add correction (4.1.5 and 3.9.1 of G.729). More... | |
| float | ff_amr_set_fixed_gain (float fixed_gain_factor, float fixed_mean_energy, float *prediction_error, float energy_mean, const float *pred_table) |
| Calculate fixed gain (part of section 6.1.3 of AMR spec) More... | |
| void | ff_decode_pitch_lag (int *lag_int, int *lag_frac, int pitch_index, const int prev_lag_int, const int subframe, int third_as_first, int resolution) |
| Decode the adaptive codebook index to the integer and fractional parts of the pitch lag for one subframe at 1/3 fractional precision. More... | |
| void ff_acelp_update_past_gain | ( | int16_t * | quant_energy, |
| int | gain_corr_factor, | ||
| int | log2_ma_pred_order, | ||
| int | erasure | ||
| ) |
Update past quantized energies.
| [in,out] | quant_energy | past quantized energies (5.10) |
| gain_corr_factor | gain correction factor | |
| log2_ma_pred_order | log2() of MA prediction order | |
| erasure | frame erasure flag |
If frame erasure flag is not equal to zero, memory is updated with averaged energy, attenuated by 4dB: max(avg(quant_energy[i])-4, -14), i=0,ma_pred_order
In normal mode memory is updated with Er - Ep = 20 * log10(gain_corr_factor)
Definition at line 32 of file acelp_pitch_delay.c.
Referenced by decode_frame().
| int16_t ff_acelp_decode_gain_code | ( | AudioDSPContext * | adsp, |
| 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 | max_pred_order | ||
| ) |
Decode the adaptive codebook gain and add correction (4.1.5 and 3.9.1 of G.729).
| adsp | initialized audio DSP context | |
| gain_corr_factor | gain correction factor (2.13) | |
| fc_v | fixed-codebook vector (2.13) | |
| mr_energy | mean innovation energy and fixed-point correction (7.13) | |
| [in,out] | quant_energy | past quantized energies (5.10) |
| subframe_size | length of subframe |
The routine implements equations 69, 66 and 71 of the G.729 specification (3.9.1)
Em - mean innovation energy (dB, constant, depends on decoding algorithm) Ep - mean-removed predicted energy (dB) Er - mean-removed innovation energy (dB) Ei - mean energy of the fixed-codebook contribution (dB) N - subframe_size M - MA (Moving Average) prediction order gc - fixed-codebook gain gc_p - predicted fixed-codebook gain
Fixed codebook gain is computed using predicted gain gc_p and correction factor gain_corr_factor as shown below:
gc = gc_p * gain_corr_factor
The predicted fixed codebook gain gc_p is found by predicting the energy of the fixed-codebook contribution from the energy of previous fixed-codebook contributions.
mean = 1/N * sum(i,0,N){ fc_v[i] * fc_v[i] }
Ei = 10log(mean)
Er = 10log(1/N * gc^2 * mean) - Em = 20log(gc) + Ei - Em
Replacing Er with Ep and gc with gc_p we will receive:
Ep = 10log(1/N * gc_p^2 * mean) - Em = 20log(gc_p) + Ei - Em
and from above:
gc_p = 10^((Ep - Ei + Em) / 20)
Ep is predicted using past energies and prediction coefficients:
Ep = sum(i,0,M){ ma_prediction_coeff[i] * quant_energy[i] }
gc_p in fixed-point arithmetic is calculated as following:
mean = 1/N * sum(i,0,N){ (fc_v[i] / 2^13) * (fc_v[i] / 2^13) } =
= 1/N * sum(i,0,N) { fc_v[i] * fc_v[i] } / 2^26
Ei = 10log(mean) = -10log(N) - 10log(2^26) +
+ 10log(sum(i,0,N) { fc_v[i] * fc_v[i] })
Ep - Ei + Em = Ep + Em + 10log(N) + 10log(2^26) -
- 10log(sum(i,0,N) { fc_v[i] * fc_v[i] }) =
= Ep + mr_energy - 10log(sum(i,0,N) { fc_v[i] * fc_v[i] })
gc_p = 10 ^ ((Ep - Ei + Em) / 20) =
= 2 ^ (3.3219 * (Ep - Ei + Em) / 20) = 2 ^ (0.166 * (Ep - Ei + Em))
where
mr_energy = Em + 10log(N) + 10log(2^26)
Definition at line 53 of file acelp_pitch_delay.c.
Referenced by decode_frame().
| float ff_amr_set_fixed_gain | ( | float | fixed_gain_factor, |
| float | fixed_mean_energy, | ||
| float * | prediction_error, | ||
| float | energy_mean, | ||
| const float * | pred_table | ||
| ) |
Calculate fixed gain (part of section 6.1.3 of AMR spec)
| fixed_gain_factor | gain correction factor |
| fixed_mean_energy | mean decoded algebraic codebook vector energy |
| prediction_error | vector of the quantified predictor errors of the four previous subframes. It is updated by this function. |
| energy_mean | desired mean innovation energy |
| pred_table | table of four moving average coefficients |
Definition at line 86 of file acelp_pitch_delay.c.
Referenced by amrnb_decode_frame(), amrwb_decode_frame(), and decode_frame().
| void ff_decode_pitch_lag | ( | int * | lag_int, |
| int * | lag_frac, | ||
| int | pitch_index, | ||
| const int | prev_lag_int, | ||
| const int | subframe, | ||
| int | third_as_first, | ||
| int | resolution | ||
| ) |
Decode the adaptive codebook index to the integer and fractional parts of the pitch lag for one subframe at 1/3 fractional precision.
The choice of pitch lag is described in 3GPP TS 26.090 section 5.6.1.
| lag_int | integer part of pitch lag of the current subframe |
| lag_frac | fractional part of pitch lag of the current subframe |
| pitch_index | parsed adaptive codebook (pitch) index |
| prev_lag_int | integer part of pitch lag for the previous subframe |
| subframe | current subframe number |
| third_as_first | treat the third frame the same way as the first |
Definition at line 107 of file acelp_pitch_delay.c.
Referenced by decode_frame(), and decode_pitch_vector().
1.8.17