b5b9add7f2346ca523137521945936ab59bb2c9b

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 */

23 #ifndef FFMPEG_ACELP_PITCH_DELAY_H

24 #define FFMPEG_ACELP_PITCH_DELAY_H

26 #include <stdint.h>

28 #define PITCH_DELAY_MIN 20

29 #define PITCH_DELAY_MAX 143

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 */

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 */

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 */

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 */

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 */

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 */

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 */