SD2

SD2 refers to Sound Designer II, a digital audio sample file format developed by Digidesign for their early sampling and editing systems. SD2 files typically contain raw audio sample data along with metadata describing sample rate, bit depth, loop points, root note, tuning, and loop parameters. The format was widely used on Macintosh-based hardware in the late 1980s and 1990s, often in conjunction with Digidesign's sample playback devices and software, including Sound Designer and early Pro Tools environments. The SD2 format supported samples of varying lengths and multiple channels (mono or stereo), enabling simple sample-based instrument libraries for hardware samplers and software synths of the era.

In practice, SD2 served as a relatively proprietary ecosystem centered on Digidesign and its partners. Over time, more open formats such as AIFF and WAV gained prominence, and improved sampling architectures led to broader compatibility. Modern workflows generally favor converting SD2 samples to universally supported formats when migrating libraries. Some modern audio software can read SD2 files directly or via import tools, but support can vary across platforms.

Today, SD2 is primarily of historical interest, representing an early stage in computer-based sampling and the forerunner to more flexible sample formats. It is often encountered in vintage sample libraries and archival collections, and knowledge of the format is useful for audio historians and professionals restoring older Pro Tools projects.