From Sega Retro

X3V is a voice bank format developed by nineko for use in his xm3smps music conversion tool. It can contain up to 255 YM2612 voices formatted according to the SMPS specifications; additionally, it can store a description for each voice. Other than xm3smps, Puto's xm4smps can also read and write X3V voice banks.

File Structure

The internal structure of an X3V voice bank is simple. The first byte specifies how many voices there are in the bank (0 to 255); after that, the actual voices begin, in the following format:

Voice Description length Description
25 bytes
1 byte
0 to 255 bytes

Opposed to YMX files, which store voices in the format used by Sonic 2, X3V banks store voices in the format used by all the other Sonic games.