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.

Additional documentation by barncastle, Special thanks to them! https://reshax.com/topic/1020-help-issues-decompressing-unknown-lzo-compressed-data-ghx2/

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	Calculated using a custom version of Fletcher-32 that uses 0x15B0 sized blocks

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

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"	File identifier
ASCII	"0153" / "0110"	Replayer version string, minimum is 0110

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.

EXPP chunk

Type	Name	Comment
ASCII	"EXPP"	Referenced during export
uint32	Size of data
char[*]	Data	Length of data is dictated by the below dword

AUTH chunk

Type	Name	Comment
ASCII	"AUTH"
uint32	Length of author's name
char[*]	Author's name	Length of name is dictated by the below word

INST chunk

Type	Name
ASCII	"INST"
uint32	Size of instrument data

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"
uint32	Size of wave data