iPod won't accept a WAV file - why??

I have a 4th-gen iPod nano, and I need to copy some WAV files onto it. However, when I sync the iPod, the WAV files don't appear on the iPod (even though I have not received an error message about copying them). The WAV files are ones I recorded myself, and edited in the program GoldWave. They are PCM signed 24 bit mono files. Does the iPod nano not accept WAV files in the PCM signed 24 bit mono format? If not, how do I need to format the files in order to be able to play them back on my iPod? Thanks very much for any help you can give me!!!