Hi Esther:
I'm not sure on the encoding bit rate but I just recently up loaded a PDF manual, set the pace I wanted and in about 10 MIN or so, a 1 HR file was produced. There were 2 versions created, 1 for I-Pod, M4B, I believe is the formating and MP3. If I had to guess, I would say the top quality voice is about 96 bit rate-but that's just a guess.
The Dave American Voice, is a little gravelly, not Alex VO. LOL Hope this helps: Cheers: Mike
