sox "unknown file type" problem.

[rvclayton@acm.org (R. Clayton)]

I've installed sox on a debian testing system updated weekly:

 ku dpkg-query -l *sox*
 Desired=Unknown/Install/Remove/Purge/Hold
 | Status=Not/Installed/Config-files/Unpacked/Failed-config/Half-installed
 |/ Err?=(none)/Hold/Reinst-required/X=both-problems (Status,Err: uppercase=bad)
 ||/ Name           Version        Description
 +++-==============-==============-============================================
 un  libsox-fmt-all <none>         (no description available)
 ii  libsox-fmt-als 14.0.0-4       SoX alsa format I/O library
 ii  libsox-fmt-ao  14.0.0-4       SoX Libao format I/O library
 ii  libsox-fmt-bas 14.0.0-4       Minimal set of SoX format libraries
 ii  libsox-fmt-oss 14.0.0-4       SoX OSS format I/O library
 ii  libsox0        14.0.0-4       SoX library
 ii  sox            14.0.0-4       Swiss army knife of sound processing

 ku 

and it doesn't work:

  ku file gargantula.mp3 
  gargantula.mp3: Audio file with ID3 version 22.0 tag, MP3 encoding

  ku sox gargantula.mp3 gargantula.ogg
  sox soxio: Failed reading `gargantula.mp3': unknown file type `mp3'

  ku sox -t mp3 gargantula.mp3 gargantula.ogg
  sox soxio: Failed reading `gargantula.mp3': unknown file type `mp3'

  ku 

Searching around a bit turns up something recent having to do with libraries
but I can't make much sense of it and it seems related to building sox from
source.

What are the steps I need to take to get sox working?