libavcodec/acelp_pitch_delay.h

   1 /*
   2  * gain code, gain pitch and pitch delay decoding
   3  *
   4  * Copyright (c) 2008 Vladimir Voroshilov
   5  *
   6  * This file is part of FFmpeg.
   7  *
   8  * FFmpeg is free software; you can redistribute it and/or
   9  * modify it under the terms of the GNU Lesser General Public
  10  * License as published by the Free Software Foundation; either
  11  * version 2.1 of the License, or (at your option) any later version.
  12  *
  13  * FFmpeg is distributed in the hope that it will be useful,
  14  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  16  * Lesser General Public License for more details.
  17  *
  18  * You should have received a copy of the GNU Lesser General Public
  19  * License along with FFmpeg; if not, write to the Free Software
  20  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  21  */
  22
  23 #ifndef AVCODEC_ACELP_PITCH_DELAY_H
  24 #define AVCODEC_ACELP_PITCH_DELAY_H
  25
  26 #include <stdint.h>
  27
  28 #define PITCH_DELAY_MIN             20
  29 #define PITCH_DELAY_MAX             143
  30
  31 /**
  32  * \brief Decode pitch delay of the first subframe encoded by 8 bits with 1/3
  33  *        resolution.
  34  * \param ac_index adaptive codebook index (8 bits)
  35  *
  36  * \return pitch delay in 1/3 units
  37  *
  38  * Pitch delay is coded:
  39  *    with 1/3 resolution, 19  < pitch_delay <  85
  40  *    integers only,       85 <= pitch_delay <= 143
  41  */
  42 int ff_acelp_decode_8bit_to_1st_delay3(int ac_index);
  43
  44 /**
  45  * \brief Decode pitch delay of the second subframe encoded by 5 or 6 bits
  46  *        with 1/3 precision.
  47  * \param ac_index adaptive codebook index (5 or 6 bits)
  48  * \param pitch_delay_min lower bound (integer) of pitch delay interval
  49  *                      for second subframe
  50  *
  51  * \return pitch delay in 1/3 units
  52  *
  53  * Pitch delay is coded:
  54  *    with 1/3 resolution, -6 < pitch_delay - int(prev_pitch_delay) < 5
  55  *
  56  * \remark The routine is used in G.729 @8k, AMR @10.2k, AMR @7.95k,
  57  *         AMR @7.4k for the second subframe.
  58  */
  59 int ff_acelp_decode_5_6_bit_to_2nd_delay3(
  60         int ac_index,
  61         int pitch_delay_min);
  62
  63 /**
  64  * \brief Decode pitch delay with 1/3 precision.
  65  * \param ac_index adaptive codebook index (4 bits)
  66  * \param pitch_delay_min lower bound (integer) of pitch delay interval for
  67  *                      second subframe
  68  *
  69  * \return pitch delay in 1/3 units
  70  *
  71  * Pitch delay is coded:
  72  *    integers only,          -6  < pitch_delay - int(prev_pitch_delay) <= -2
  73  *    with 1/3 resolution,    -2  < pitch_delay - int(prev_pitch_delay) <  1
  74  *    integers only,           1 <= pitch_delay - int(prev_pitch_delay) <  5
  75  *
  76  * \remark The routine is used in G.729 @6.4k, AMR @6.7k, AMR @5.9k,
  77  *         AMR @5.15k, AMR @4.75k for the second subframe.
  78  */
  79 int ff_acelp_decode_4bit_to_2nd_delay3(
  80         int ac_index,
  81         int pitch_delay_min);
  82
  83 /**
  84  * \brief Decode pitch delay of the first subframe encoded by 9 bits
  85  *        with 1/6 precision.
  86  * \param ac_index adaptive codebook index (9 bits)
  87  * \param pitch_delay_min lower bound (integer) of pitch delay interval for
  88  *                      second subframe
  89  *
  90  * \return pitch delay in 1/6 units
  91  *
  92  * Pitch delay is coded:
  93  *    with 1/6 resolution,  17  < pitch_delay <  95
  94  *    integers only,        95 <= pitch_delay <= 143
  95  *
  96  * \remark The routine is used in AMR @12.2k for the first and third subframes.
  97  */
  98 int ff_acelp_decode_9bit_to_1st_delay6(int ac_index);
  99
 100 /**
 101  * \brief Decode pitch delay of the second subframe encoded by 6 bits
 102  *        with 1/6 precision.
 103  * \param ac_index adaptive codebook index (6 bits)
 104  * \param pitch_delay_min lower bound (integer) of pitch delay interval for
 105  *                      second subframe
 106  *
 107  * \return pitch delay in 1/6 units
 108  *
 109  * Pitch delay is coded:
 110  *    with 1/6 resolution, -6 < pitch_delay - int(prev_pitch_delay) < 5
 111  *
 112  * \remark The routine is used in AMR @12.2k for the second and fourth subframes.
 113  */
 114 int ff_acelp_decode_6bit_to_2nd_delay6(
 115         int ac_index,
 116         int pitch_delay_min);
 117
 118 /**
 119  * \brief Update past quantized energies
 120  * \param quant_energy [in/out] past quantized energies (5.10)
 121  * \param gain_corr_factor gain correction factor
 122  * \param log2_ma_pred_order log2() of MA prediction order
 123  * \param erasure frame erasure flag
 124  *
 125  * If frame erasure flag is not equal to zero, memory is updated with
 126  * averaged energy, attenuated by 4dB:
 127  *     max(avg(quant_energy[i])-4, -14), i=0,ma_pred_order
 128  *
 129  * In normal mode memory is updated with
 130  *     Er - Ep = 20 * log10(gain_corr_factor)
 131  *
 132  * \remark The routine is used in G.729 and AMR (all modes).
 133  */
 134 void ff_acelp_update_past_gain(
 135         int16_t* quant_energy,
 136         int gain_corr_factor,
 137         int log2_ma_pred_order,
 138         int erasure);
 139
 140 /**
 141  * \brief Decode the adaptive codebook gain and add
 142  *        correction (4.1.5 and 3.9.1 of G.729).
 143  * \param gain_corr_factor gain correction factor (2.13)
 144  * \param fc_v fixed-codebook vector (2.13)
 145  * \param mr_energy mean innovation energy and fixed-point correction (7.13)
 146  * \param quant_energy [in/out] past quantized energies (5.10)
 147  * \param subframe_size length of subframe
 148  * \param ma_pred_order MA prediction order
 149  *
 150  * \return quantized fixed-codebook gain (14.1)
 151  *
 152  * The routine implements equations 69, 66 and 71 of the G.729 specification (3.9.1)
 153  *
 154  *    Em   - mean innovation energy (dB, constant, depends on decoding algorithm)
 155  *    Ep   - mean-removed predicted energy (dB)
 156  *    Er   - mean-removed innovation energy (dB)
 157  *    Ei   - mean energy of the fixed-codebook contribution (dB)
 158  *    N    - subframe_size
 159  *    M    - MA (Moving Average) prediction order
 160  *    gc   - fixed-codebook gain
 161  *    gc_p - predicted fixed-codebook gain
 162  *
 163  *    Fixed codebook gain is computed using predicted gain gc_p and
 164  *    correction factor gain_corr_factor as shown below:
 165  *
 166  *        gc = gc_p * gain_corr_factor
 167  *
 168  *    The predicted fixed codebook gain gc_p is found by predicting
 169  *    the energy of the fixed-codebook contribution from the energy
 170  *    of previous fixed-codebook contributions.
 171  *
 172  *        mean = 1/N * sum(i,0,N){ fc_v[i] * fc_v[i] }
 173  *
 174  *        Ei = 10log(mean)
 175  *
 176  *        Er = 10log(1/N * gc^2 * mean) - Em = 20log(gc) + Ei - Em
 177  *
 178  *    Replacing Er with Ep and gc with gc_p we will receive:
 179  *
 180  *        Ep = 10log(1/N * gc_p^2 * mean) - Em = 20log(gc_p) + Ei - Em
 181  *
 182  *    and from above:
 183  *
 184  *        gc_p = 10^((Ep - Ei + Em) / 20)
 185  *
 186  *    Ep is predicted using past energies and prediction coefficients:
 187  *
 188  *        Ep = sum(i,0,M){ ma_prediction_coeff[i] * quant_energy[i] }
 189  *
 190  *    gc_p in fixed-point arithmetic is calculated as following:
 191  *
 192  *        mean = 1/N * sum(i,0,N){ (fc_v[i] / 2^13) * (fc_v[i] / 2^13) } =
 193  *        = 1/N * sum(i,0,N) { fc_v[i] * fc_v[i] } / 2^26
 194  *
 195  *        Ei = 10log(mean) = -10log(N) - 10log(2^26) +
 196  *        + 10log(sum(i,0,N) { fc_v[i] * fc_v[i] })
 197  *
 198  *        Ep - Ei + Em = Ep + Em + 10log(N) + 10log(2^26) -
 199  *        - 10log(sum(i,0,N) { fc_v[i] * fc_v[i] }) =
 200  *        = Ep + mr_energy - 10log(sum(i,0,N) { fc_v[i] * fc_v[i] })
 201  *
 202  *        gc_p = 10 ^ ((Ep - Ei + Em) / 20) =
 203  *        = 2 ^ (3.3219 * (Ep - Ei + Em) / 20) = 2 ^ (0.166 * (Ep - Ei + Em))
 204  *
 205  *    where
 206  *
 207  *        mr_energy = Em + 10log(N) + 10log(2^26)
 208  *
 209  * \remark The routine is used in G.729 and AMR (all modes).
 210  */
 211 int16_t ff_acelp_decode_gain_code(
 212     int gain_corr_factor,
 213     const int16_t* fc_v,
 214     int mr_energy,
 215     const int16_t* quant_energy,
 216     const int16_t* ma_prediction_coeff,
 217     int subframe_size,
 218     int max_pred_order);
 219
 220 #endif /* AVCODEC_ACELP_PITCH_DELAY_H */