Vox Studio supports 2 companding and 3 compression formats used by NMS (Natural MicroSystems) cards (see below). Stand-alone NMS files usually carry the ".vce" extension while indexed files usually carry the ".vox" extension. Vox files usually (but not always) contain multiple prompts. NMS vox files that contain only a single prompt are called single-prompt vox files in Vox Studio. Both ".vce" and ".vox" files have a file header. Vox Studio converts to and from NMS ".vce" files or to and from NMS single-prompt ".vox" files. Vox Studio has a separate command to group prompt files into indexed ".vox" files or ungroup ".vox" indexed files to stand alone files.
To summarize: NMS ".vce" files are non-indexed files and contain a single voice prompt. NMS ".vox" files are indexed files and can contain either multiple voice prompts or a single prompt. Vox Studio converts directly from other single-prompt formats (".wav" for instance) to ".vce" files or to "single-prompt vox" files. To produce "multi-prompt vox" files you have to use the "Group NMS" command that does on-the-fly conversion to NMS formats. It is thus possible to group ".wav" files, for instance, into a vox file; conversion is done automatically by Vox Studio.
Companding laws
Vox Studio supports the NMS file format with both A-law and Mu-law companding at 8,000 samples per second.
NMS ADPCM
Vox Studio supports the NMS file formats with ADPCM compression at 32 KBps, 24 KBps and 16 KBps, all at 8,000 samples per second. 32 KBps is by far the most popular coding scheme for NMS cards.