.SD File Extension
File Type 1ESPS Sampled Data File
What is an SD file?
Audio format created by Entropic Research Laboratories and used for the WAVES+ display program, ESPS signal processing library, and the HTK speech recognition toolkit
Programs that open SD files
File Type 2Sound Designer Audio File
.SD File Association 2
Audio format used by Sound Designer, one of the first popular audio-editing programs available for the Mac