Sound files can be in Windows .WAV format, monaural or stereophonic, 8 or 16 bits per sample, at 8000, 11025, 22050, or 44100 samples per second (if you're making a file expressly to be sent by Speak Freely, for best sound quality and efficiency select 8000 16 bit monaural samples per second). For compatibility with Unix and the World-Wide Web, you can also send files in Sun Audio File or raw Sun Audio formats (.AU files). Such files are assumed to be recorded at 8000 8 bit monaural samples per second, using mu-law encoding.