Are the Bin Laden audio tapes authentic?

Some very worrying points raised by Jason Kernahan here:
But we actually have no reason whatsoever to believe that these tapes are authentic. While there have been reports of scientific voice analyses performed on them, these studies have been invariably done by CIA experts. In fact, on only one occasion was an independent analysis done. And while US officials were certain of that tape’s authenticity, Swedish scientists were equally convinced that it was a fake.