GAX .ghx2 project file documentation (WIP)

ghx2_docs.md

Shin'en GAX Sound Engine - .ghx2 file format

The .ghx2 file format is typically the original project file, created with the GHX2 editor program. The GAXPlay program is the only program available that can read these files. The documentation is incomplete since there are a ton of unknowns, but I'll post what I have here.

Markdown formatting taken from https://gist.github.com/loveemu/9b3063ffd9a76cb18e379324e43f3251

File header

GHXC chunk

Type	Name	Comment
ASCII	"GHXC"	Might stand for "GHX Compressed"
uint32	Uncompressed data size	Size of the "LZOD" chunk when uncompressed
uint32	Uncompressed data checksum[?]	Actual purpose unknown

LZOD chunk

Uses a currently unknown (likely proprietary) version of Lempel-Ziv-Oberhumer compression.

Type	Name	Comment
ASCII	"LZOD"	"Lempel-Ziv-Oberhumer Data"
uint32	Compressed data size	Size of the LZOD chunk itself
uint16	Unknown	Values I've seen are 0x1900, 0x1500, etc

LZOD chunk data

Extremely heavy WIP. Since the LZOD compression type is unknown, the fields are pure guesswork.

File version

Type	Name	Comment
ASCII	"GHX2", "0153"	Maybe for distinguishing between different GHX2 file revisions?

SONG chunk

Header chunk

Type	Name
ASCII	"SONG"
uint32	Song bank data size(?)

Data chunk (incomplete)

Type	Name	Comment
Pascal-string	Song title
uint32	Number of channels
uint32	Number of steps per pattern
unknown	unknown
uint16	Unknown pointer	Pointer to somewhere in song data
uint16	Unknown pointer #2	Pointer to somewhere in song data
uint16	Unknown pointer #3
uint32	Master volume (amplification)
uint16	Music mix rate
uint16	FX mix rate
uint8	FX channel count

The rest could very well be pattern data + order list data.

EXP chunk

Type	Name	Comment
ASCII	"EXP"	Could mean "Export" or "External Properties"
uint16	Unknown pointer
unknown	unknown	Seen strings like "Song", and a uint32 pointer
Pascal-string	Author's full name

INST chunk

Type	Name
ASCII	"INST"

Instrument data (incomplete)

Type	Name	Comment
uint32	Pointer to wave data
unknown	unknown
Pascal-string	Instrument name	Example -> "frenchhorn1 copy (6)"
unknown	unknown

WAVE chunk

Type	Name
ASCII	"WAVE"

TBA

Footer

Type	Name	Comment
unknown	unknown
uint8[5]	unknown	0x0000110000