In order to utilize mod_native_file, I converted the original L16 8000Hz audio into G711 with sox: sox ${SRCFILE} -t raw -r 8k -b 8 -c 1 -e u-law ${DSTDIR}/${BASENAME}.PCMU I just discovered that if I do this command twice and compare resulting files, they differ. They also differ if I take 44100Hz source audio. Anyone got a clue what's going on? FreeSWITCH is always producing the same bitstream when converting L16 to G711.