Convert spx to nist

What is the difference between .spx and .nist?

Description: Audio file compressed using Speex compression and saved in the Ogg Vorbis container format; designed as an audio compression format specifically for speech; compresses voice at 2 to 44 kbps and supports 8 kHz, 16 kHz, and 32 kHz compression in the same bitstream.; 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.