Not exactly sure. one thing to note is that in general, you should always make the files mono. Speech really is always mono, there isn't anything capable of adding another channel of anything interesting. So the only time you should ever be making stereo files is if the eventual user of the audio file requires it. For example, there may be some CD burning software out there that will only recognize stereo files. Unless you have that specific need, then all you are doing is wasting file space, since making them stereo really should only be making both channels the same.