SDII
From WikiRecording
Sound Designer II or .SDII is an audio file format, originally developed by Digidesign. Sound Designer I, a monophonic audio format, was the precursor to SDII, which was both monophonic and stereo phonic. It was originally created to be a sample-editing platform that interfaced with digital sampling instruments of the day. SDII was then adopted for use in DigiDesign's Sound Tools, which became Sound Designer II, which was itself the precursor to ProTools.
SDII files store sample rate and bit depth information. The tracks of a stereophonic SDII file are separated into left and right matched files like this: Guitar-001-left, Guitar-001-right, Guitar-002-left, Guitar-002-right, etc...
The SDII file has diminished in use over the years, losing ground to AIFF and WAV audio formats, but it is still popular in high end DAW software, such as ProTools and Digital Performer, possibly because of its advantages as a non-destructive audio file format. Sound Designer II files store all sound samples in the data fork and all sound parameters in the resource fork. This is extremely convenient for sound data where the data fork may grow to a hundred megabytes or more. Regardless of the size of the data fork you can add, delete, and modify sound parameters at will without compacting the sound data or moving it around the disk (and extremely time consuming procedure if the file is 100 MB). SDII has the added advantage that it can contain region/song position information.
When used on a PC, the file often must use the extension of ".sd2".
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