Audio format created by Entropic Research Laboratories and used for the WAVES+ display program, ESPS signal processing library, and the HTK speech recognition toolkit
The SD file extension is used for shape files in Microsoft Train Simulator. A .sd file contains shape defintion data.
The SD file extension is also used in the Mechanical Toys design technology program from Focus Educational Software. These files contain CAD drawing created and saved in the program.
Audio format used by Sound Designer, one of the first popular audio-editing programs available for the Mac