SD2 is the file extension that is most often used by the Avid Pro Tools audio editor. SD2 files are files that store audio data generated during the recording of audio material by the program in the Sound Designer 2 format. They can store mono and stereo material with a bit resolution of 8 and 16 bits.

The SD2 format was developed by Digidesign for Macintosh computers, but is used to exchange audio data between applications.