ADX
From Sega Retro
The ADX Codec, made by CRI Middleware Co. Ltd., is a multi-streaming system and provides audio compression features while using minimum CPU load. While playing back music, it can play back talking voice or read game data as well. Music playback and data reading from a disc can be executed independently and asynchronously. Any type of data can be read, from audio data to graphics or programs.
ADX allows repeated playback of arbitrary intervals in general wave data. You can create arbitrary looped digital audio sequences, without staying within the MIDI environment. For this reason, the format is often coveted as the "ideal" rip for video game music. ADX also works with the Sofdec movie codec, providing its audio elements. ADX is a 4-bit ADPCM format and can store mono or stereo audio. One of the first games to use ADX was Burning Rangers, on the Sega Saturn.