sox resources/my-audio.wav --channels=1 --bits=16 --rate=16000 --endian=little resources/my-audio.flac
Figured it out... turns out the sox command to convert the wav on the support page isn't quite right. Here is the command that worked for me:
sox resources/my-audio.wav \ --channels=1 \ --bits=16 \ --rate=16000 \ --encoding=signed-integer \ --endian=little resources/my-audio.raw
The two key differences with my original command were (1) add the
--encoding=signed-integer (thanks to this) and (2) use the
.raw extension on the output filename.