PVF is a special low-bandwidth ADPCM-based digital audio format for recording and storing human speech. A .pvf file contains digitally recorded speech in the PVF format. Such .pvf files were mainly used with legacy voice modems and software-based answering machines. Often, to be used with a specific modem, a .pvf file would have to be converted into the device-specific RMD format. Currently, PVF audio files can still be played with several major media players as well as converted into other formats (like WAV) with multi-format converter tools.
SPHERE (SPeech HEader Resources) is a file format defined by NIST (National Institute of Standards and Technology) and is used with speech audio. SoX can read these files when they contain μ-law and PCM data. It will ignore any header information that says the data is compressed using shorten compression and will treat the data as either μ-law or PCM. This will allow SoX and the command line shorten program to be run together using pipes to encompasses the data and then pass the result to SoX for processing.