First download FFXIII-2-Music-Mod by amcolas:

DOWNLOAD LINK: https://github.com/amcolash/FFXIII-2-Music-Mod/releases/download/v1.1/FFXIII-2-Music-Mod-v1.1.zip

Then download batch files for FFXIII from Here[drive.google.com]

Copy batch files to FFXIII-2-Music-Mod.

- Make a backup from "filelistc.win32.bin" and "white_imgc.win32" from "FINAL FANTASY XIII\white_data\sys" to somewhere safe.

- Copy "filelistc.win32.bin" and "white_imgc.win32" to this folder
- Open BGM Adjustment (JP)
Type in your desired gain (between 0.0 Lowest ~ 2.0 Highest):

[0.5] -> 50% of original audio
[0.7] -> 70% of original audio
[1.2] -> 120% of original audio

- Copy back and replace "filelistc.win32.bin" and "white_imgc.win32" to "FINAL FANTASY XIII\white_data\sys"

- Always copy fresh original files to this folder if you want to try different config.

- Make a backup from "filelistu.win32.bin" and "white_imgu.win32" from "FINAL FANTASY XIII\white_data\sys" to somewhere safe.

- Copy "filelistu.win32.bin" and "white_imgu.win32" to this folder
- Open BGM Adjustment (EN)
Type in your desired gain (between 0.0 Lowest ~ 2.0 Highest):

[0.5] -> 50% of original audio
[0.7] -> 70% of original audio
[1.2] -> 120% of original audio

- Copy back and replace "filelistu.win32.bin" and "white_imgu.win32" to "FINAL FANTASY XIII\white_data\sys"

- Always copy fresh original files to this folder if you want to try different config.

I've just made some changes to batch files to makes it work with FFXIII.

Main guide for FFXIII-2 created by amcolash:

https://gtm.steamproxy.vip/app/292140/discussions/0/1694914736006118287

If this guide helps you please don't forget to rate it. thank you.