I'm trying to transcode a .wav to a .gsm using SOX v14.0.1. What I get is a completely garbled when using playback in FreeSWITCH. I have verified that at least one other application (Quicktime Player) can in fact play the resulting .gsm file. I have tried the following: sox william.wav -t gsm william.gsm sox william.wav -t gsm -r 8000 william.gsm resample -ql sox william.wav -t gsm -r 8000 -c1 william.gsm resample -ql And I am playing the file using: originate sofia/internal/1000@192.168.1.1 &playback(/home/user/william.gsm) Other formats such as uLaw and aLaw (-t ul and -t al, respectively) seem to work fine. Does anyone know of a set of parameters for SOX that will make this work? At the end of the day, I just want it to work, so if anyone can recommend any other known/good command line tools to encode GSM that would be fine too.