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

// Compiler optimizer (at least I think so :)) generated following tables to speedup volume calculation for left & right volume.

const uint16_t m_AKAO_VOLUME_TABLE_L[256] = {
  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,
  0x0000, 0xffff, 0xfffc, 0xfff7, 0xfff0, 0xffe7, 0xffdc, 0xffcf,
  0xffc0, 0xffaf, 0xff9c, 0xff87, 0xff70, 0xff57, 0xff3c, 0xff1f,
  0xff00, 0xfedf, 0xfebc, 0xfe97, 0xfe70, 0xfe47, 0xfe1c, 0xfdef,
  0xfdc0, 0xfd8f, 0xfd5c, 0xfd27, 0xfcf0, 0xfcb7, 0xfc7c, 0xfc3f,
  0xfc00, 0xfbbf, 0xfb7c, 0xfb37, 0xfaf0, 0xfaa7, 0xfa5c, 0xfa0f,
  0xf9c0, 0xf96f, 0xf91c, 0xf8c7, 0xf870, 0xf817, 0xf7bc, 0xf75f,
  0xf700, 0xf69f, 0xf63c, 0xf5d7, 0xf570, 0xf507, 0xf49c, 0xf42f,
  0xf3c0, 0xf34f, 0xf2dc, 0xf267, 0xf1f0, 0xf177, 0xf0fc, 0xf07f,
  0x1000, 0x1081, 0x1104, 0x1189, 0x1210, 0x1299, 0x1324, 0x13b1,
  0x1440, 0x14d1, 0x1564, 0x15f9, 0x1690, 0x1729, 0x17c4, 0x1861,
  0x1900, 0x19a1, 0x1a44, 0x1ae9, 0x1b90, 0x1c39, 0x1ce4, 0x1d91,
  0x1e40, 0x1ef1, 0x1fa4, 0x2059, 0x2110, 0x21c9, 0x2284, 0x2341,
  0x2400, 0x24c1, 0x2584, 0x2649, 0x2710, 0x27d9, 0x28a4, 0x2971,
  0x2a40, 0x2b11, 0x2be4, 0x2cb9, 0x2d90, 0x2e69, 0x2f44, 0x3021,
  0x3100, 0x31e1, 0x32c4, 0x33a9, 0x3490, 0x3579, 0x3664, 0x3751,
  0x3840, 0x3931, 0x3a24, 0x3b19, 0x3c10, 0x3d09, 0x3e04, 0x3f01
};

const uint16_t m_AKAO_VOLUME_TABLE_R[256] = {
  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,
  0x3f01, 0x3e04, 0x3d09, 0x3c10, 0x3b19, 0x3a24, 0x3931, 0x3840,
  0x3751, 0x3664, 0x3579, 0x3490, 0x33a9, 0x32c4, 0x31e1, 0x3100,
  0x3021, 0x2f44, 0x2e69, 0x2d90, 0x2cb9, 0x2be4, 0x2b11, 0x2a40,
  0x2971, 0x28a4, 0x27d9, 0x2710, 0x2649, 0x2584, 0x24c1, 0x2400,
  0x2341, 0x2284, 0x21c9, 0x2110, 0x2059, 0x1fa4, 0x1ef1, 0x1e40,
  0x1d91, 0x1ce4, 0x1c39, 0x1b90, 0x1ae9, 0x1a44, 0x19a1, 0x1900,
  0x1861, 0x17c4, 0x1729, 0x1690, 0x15f9, 0x1564, 0x14d1, 0x1440,
  0x13dc, 0x1324, 0x1299, 0x1210, 0x1189, 0x1104, 0x1081, 0x1000,
  0xf07f, 0xf0fc, 0xf177, 0xf1f0, 0xf267, 0xf2dc, 0xf34f, 0xf3c0,
  0xf42f, 0xf49c, 0xf507, 0xf570, 0xf5d7, 0xf63c, 0xf69f, 0xf700,
  0xf75f, 0xf7bc, 0xf817, 0xf870, 0xf8c7, 0xf91c, 0xf843, 0xf9c0,
  0xfa0f, 0xfa5c, 0xfaa7, 0xfaf0, 0xfb37, 0xfb7c, 0xfbbf, 0xfc00,
  0xfc3f, 0xfc7c, 0xfcb7, 0xfcf0, 0xfd27, 0xfd5c, 0xfd8f, 0xfdc0,
  0xfdef, 0xfe1c, 0xfe47, 0xfe70, 0xfe97, 0xfebc, 0xfedf, 0xff00,
  0xff1f, 0xff3c, 0xff57, 0xff70, 0xff87, 0xff9c, 0xffaf, 0xffc0,
  0xffcf, 0xffdc, 0xffe7, 0xfff0, 0xfff7, 0xfffc, 0xffff, 0x0000
};

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.

I'll remove these tables in future and add normal mathematical interpretation of volume calculation.