The Rockwell formats supported by Vox Studio are the ADPCM coding formats understood by the voice-enabled Rockwell modem chips. Many voice/data/fax modems on the market use the Rockwell chip-set. If your application uses one of those, this may be the format you need.
Vox Studio supports Rockwell's 4 bits ADPCM, 3 bits ADPCM and 2 bits ADPCM, all sampled at 7,200 samples/s.
When specific boards use Rockwell chips but have defined their own file formats these are treated as distinct formats by Vox Studio; for instance the Creative Labs PhoneBlaster format, which is a file format that includes a header.