Seeing that some of the google search traffic I receive is around NMS sound files, let me provide a little insight.
NMS sound files are recorded in their own proprietary format, optimized for quality and performance.
The NMS vox files are NOT the same as the Dialogic VOX files.
If you have some NMS VOX files that you need to convert, the easiest way is to convert them where some NMS software is installed (probably on the IVR machine itself).
Here's a Windows command line command to convert a folder of NMS files to WAV files:
for %1 in (\*.vox) do VCECOPY %1 %\~n1.wav -c44M16
-c44M16 means output encoding is 44mhz mono 16-bit.
If the NMS file is indexed (use VCEINFO to figure it out), meaning it contains more than one recording - kind of like a ZIP file contains a bunch of files - you'll have to use a manual technique something like the following:
vcecopy messages.vox 0.wav -c44M16 -m0,0 vcecopy messages.vox 1.wav -c44M16 -m1,0 vcecopy messages.vox 2.wav -c44M16 -m2,0
If you have a lot of files to copy, don't manually enter all the vcecopy commands. Generate the list of commands using Excel, Notepad++, PowerShell or bash.
If you need any help with decoding/encoding from one format to another, drop me a line. NMS, Dialogic, Talx, raw PCM, GSM, whatever.