Just ran into a strange problem with sox v14.0.0 on Ubuntu Hardy:
Even providing a certain type with e.g. "-t raw" gave me a similar error.sox soxio: Failed reading `silence.raw': unknown file type `auto'
[SOLUTION]
It seems that the sox requires additional libraries to be installed which were not pulled in by the package management system. Strange, because nothing's even listed in "suggested" or "recommended" packages.
Install the package "libsox-fmt-all" and the problem should be gone.