An ADX file is an audio file used by various Sega Dreamcast, PlayStation 2, GameCube, and Wii video games. It is saved in the lossy ADX storage and compression format. ADX files are commonly used for background sounds because of their ability to loop.
The ADX format can be found as an audio stream interleaved into .SFD Sofdec videos. Many of the Sonic the Hedgehog games, including the Sonic Mega Collection video game compilation, use ADX files for voice recordings and sounds. However, not many video games currently developed support the ADX format.
NOTE: The FFmpeg supports ADX files but is limited to decoding 44100 Hz ADX files.