After several years some voicebox messages of a Vbox system I’m responsible for had to be changed. Although I left a README file in the MSG directory with the commands used in the past to convert WAV to ULAW, the result wasn’t what I expected. There was an ugly cracking sound at the beginning of each ULAW file. As it wasn’t there in the intermediate AU files, it must be autovbox “adding” it.

After some research it turned out, that it is easily possible to convert WAV to ULAW in directly using SOX. The following command works like charm:

find . -name \*.wav -exec sox -V {} -r 8000 -c 1 -t ul -w {}.ulaw \;