FF7/PSX/Sound/Opcodes/0xa8aa

0xA8, 0xAA, 0xA3 (Channel Volume, Pan, Volume Modifier)

0xA8 has one 8-bit parameter, which used in calculation of base channel volume.

0xAA has one 8-bit parameter, which used in calculation of channel pan (difference between left and right channel volume).

0xA3 has one 8-bit parameter, which used in calculation of base channel volume.

Understanding of this opcodes isn't that easy, but here is what I have got:

Volume Calculation

// m_AKAO_VOLUME_TABLE_L[i] = 32768 - m_AKAO_VOLUME_TABLE_R[i];
const uint16_t m_AKAO_VOLUME_TABLE_L[128] = {
  0x7f80, 0x7e80, 0x7d80, 0x7c80, 0x7b80, 0x7a80, 0x7980, 0x7880,
  0x7780, 0x7680, 0x7580, 0x7480, 0x7380, 0x7280, 0x7180, 0x7080,
  0x6f80, 0x6e80, 0x6d80, 0x6c80, 0x6b80, 0x6a80, 0x6980, 0x6880,
  0x6780, 0x6680, 0x6580, 0x6480, 0x6380, 0x6280, 0x6180, 0x6080,
  0x5f80, 0x5e80, 0x5d80, 0x5c80, 0x5b80, 0x5a80, 0x5980, 0x5880,
  0x5780, 0x5680, 0x5580, 0x5480, 0x5380, 0x5280, 0x5180, 0x5080,
  0x4f80, 0x4e80, 0x4d80, 0x4c80, 0x4b80, 0x4a80, 0x4980, 0x4880,
  0x4780, 0x4680, 0x4580, 0x4480, 0x4380, 0x4280, 0x4180, 0x4080,
  0x3f80, 0x3e80, 0x3d80, 0x3c80, 0x3b80, 0x3a80, 0x3980, 0x3880,
  0x3780, 0x3680, 0x3580, 0x3480, 0x3380, 0x3280, 0x3180, 0x3080,
  0x2f80, 0x2e80, 0x2d80, 0x2c80, 0x2b80, 0x2a80, 0x2980, 0x2880,
  0x2780, 0x2680, 0x2580, 0x2480, 0x2380, 0x2280, 0x2180, 0x2080,
  0x1f80, 0x1e80, 0x1d80, 0x1c80, 0x1b80, 0x1a80, 0x1980, 0x1880,
  0x1780, 0x1680, 0x1580, 0x1480, 0x1380, 0x1280, 0x1180, 0x1080,
  0x0f80, 0x0e80, 0x0d80, 0x0c80, 0x0b80, 0x0a80, 0x0980, 0x0880,
  0x0780, 0x0680, 0x0580, 0x0480, 0x0380, 0x0280, 0x0180, 0x0080
};

// m_AKAO_VOLUME_TABLE_R[i] = i * 256 + 128;
const uint16_t m_AKAO_VOLUME_TABLE_R[128] = {
  0x0080, 0x0180, 0x0280, 0x0380, 0x0480, 0x0580, 0x0680, 0x0780,
  0x0880, 0x0980, 0x0a80, 0x0b80, 0x0c80, 0x0d80, 0x0e80, 0x0f80,
  0x1080, 0x1180, 0x1280, 0x1380, 0x1480, 0x1580, 0x1680, 0x1780,
  0x1880, 0x1980, 0x1a80, 0x1b80, 0x1c80, 0x1d80, 0x1e80, 0x1f80,
  0x2080, 0x2180, 0x2280, 0x2380, 0x2480, 0x2580, 0x2680, 0x2780,
  0x2880, 0x2980, 0x2a80, 0x2b80, 0x2c80, 0x2d80, 0x2e80, 0x2f80,
  0x3080, 0x3180, 0x3280, 0x3380, 0x3480, 0x3580, 0x3680, 0x3780,
  0x3880, 0x3980, 0x3a80, 0x3b80, 0x3c80, 0x3d80, 0x3e80, 0x3f80,
  0x4080, 0x4180, 0x4280, 0x4380, 0x4480, 0x4580, 0x4680, 0x4780,
  0x4880, 0x4980, 0x4a80, 0x4b80, 0x4c80, 0x4d80, 0x4e80, 0x4f80,
  0x5080, 0x5180, 0x5280, 0x5380, 0x5480, 0x5580, 0x5680, 0x5780,
  0x5880, 0x5980, 0x5a80, 0x5b80, 0x5c80, 0x5d80, 0x5e80, 0x5f80,
  0x6080, 0x6180, 0x6280, 0x6380, 0x6480, 0x6580, 0x6680, 0x6780,
  0x6880, 0x6980, 0x6a80, 0x6b80, 0x6c80, 0x6d80, 0x6e80, 0x6f80,
  0x7080, 0x7180, 0x7280, 0x7380, 0x7480, 0x7580, 0x7680, 0x7780,
  0x7880, 0x7980, 0x7a80, 0x7b80, 0x7c80, 0x7d80, 0x7e80, 0x7f80
};

left_volume = m_AKAO_VOLUME_TABLE_L[aa_parameter] * ((a8_parameter * a3_parameter * 0x7f) / 128) / 256 / 128;

right_volume = m_AKAO_VOLUME_TABLE_R[aa_parameter] * ((a8_parameter * a3_paramater * 0x7f) / 128) / 256 / 128;

If there is no A3 opcode in sequence (as in SENSUI.SND for example), default value 0x7f is used.