====== Audio Effects ======

Earthbound has four audio effect tables, each representing one SPC700 port.

Note: All addresses in this document are relative to 0x25FB42 in a vanilla ROM.

^ Port   ^ Address ^ Entries ^ Notes                                     ^
| Port 0 | $180D   | 1       | Unused, overridden by music track changes |
| Port 1 | $17D5   | 28      | Used for most music effects               |
| Port 2 | $17C5   | 8       | Only used for Giygas static               |
| Port 3 | $16C7   | 127     | Used for most sound effects               |

===== Effect Format =====


Each entry points to an effect, with the byte at offset -1 determining its type.

^ Type ^ Description                                                                                                               ^
|  00  | Same as 02? Unused?                                                                                                       |
|  02  | Single note? [NN HH II VV PP nn TT]                                                                                       |
|  04  | Sequenced [II VV PP TT seq...]                                                                                            |
|  06  | Sequenced, no staccato [II VV PP TT seq...]                                                                               |
|  08  | Assembly                                                                                                                  |
|  0A  | Like 04, but has a pointer to a second channel at offset -3                                                               |
|  0C  | Like 06, but has a pointer to a second channel at offset -3                                                               |
|  0E  | Same as 10? Unused?                                                                                                       |
|  10  | Noise, single channel. Has a pointer to GAIN data at offset -3 and a pointer to noise clocks at -5 [LL HH II VV PP CC SS] |

  * NN: Note length
  * HH: Hold length
  * II: Instrument
  * VV: Volume
  * PP: Panning
  * nn: Note
  * TT: Tuning
  * LL: Length
  * CC: Noise clock
  * SS: Speed

==== Sequence Format ====

^ Byte  ^ Description         ^
| 00    | Terminates sequence |
| 01-7F | Sets note length    |
| 80-C7 | Plays a note        |
| C8    | Tie                 |
| C9    | Rest                |
| CA    | Unknown (noise?)    |
| CB-DF | Undefined           |
| E0    | Change instrument   |
| E1    | Set panning         |
| E2-EC | Undefined           |
| ED    | Set volume          |
| EE-FF | Undefined           |

==== GAIN Format ====
???

==== Noise Clock Format ====
???