The Plain old telephone service (POTS) we are all used to is almost a hundred years old so when it comes to audio codecs you get pretty much the bottom of the barrel. When doing IVR you will want to make sure you convert all your media to the lowest common denominator, which is generally 8bit, 8Khz Mono. Doing this w/ SOX is pretty simple

for i in *.wav
 sox $i -r 8000 -U -b 8 new-files/$(basename $i)

Thats pretty much it ! If you are using OSX you can get SOX by installing Homebrew and running:

brew install sox

Hope that helps someone



John T Dyer