The voice sounds right, but video would have been more convincing. Video recorders are cheap and small. Osama could put all doubt to rest by releasing a film of him holding up a recent newspaper of Saddam's capture. Prior to Tora Bora, videos of him were the norm. What happened?

I can find only two plausible explanations. One is that Osama bin Laden is severely ill or wounded, and does not want the world to know it. The other is that he is dead, and the audio tape is faked. But how could the counterfeiter do a good enough job to fool experts?

[...]

[S]houldn't voice recognition software work reliably to identify Osama, or to reject an imitator? Unfortunately, the Al Jazeera tapes are not high quality -- probably no better than telephone sound. That's good enough to detect some kinds of deception, but not all. Here are three possibilities:

1. The tape was made by an impressionist trying to imitate bin Laden's voice. Good impressionists can mimic the tone and pacing of their subject, but they often overemphasize obvious quirks, much as a caricaturist exaggerates dominant physical features. That makes it amusing to hear, but it won't fool an analyst. Impressionists are not good at catching the more subtle features that even simple voice recognition software uses. This kind of counterfeit can almost certainly be ruled out.

2. The tape was made by cutting and pasting true excerpts from bin Laden's past speeches. Much of the tape could be unchanged from a prior recording. The tough part for the counterfeiter was adding mention of Saddam's capture [to the most recent tape, released on January 4th], where words and phrases had to be rearranged. To detect such a forgery, a good analyst would listen for discontinuities in the background noise, or small blips indicating the tape was spliced. Digital processing by the tape maker can remove such artifacts, but they leave behind their own; low-pass filters, for example, create easily detected changes in the spectrum of the background hiss. (That's why true audiophiles dislike noise suppression filters. It is readily noticed by a trained ear.) Such cutting and pasting, even with digital filtering, would have been detected by the CIA. Digital processing can be detected in other ways; for example, it sometimes generates false frequencies (called aliases). Such tampering would have raised suspicions. Therefore this scenario can probably be ruled out as well.

3. The tape was a recording of one of Osama bin Laden's sons, who was deliberately trying to sound like his father. This is, in my mind, the most likely hypothesis.

Saad bin Osama bin Laden is the third of Osama's 23 to 50 children; he is known to be in his early twenties. He has been active in al Qaeda since his pre-teen years, and was probably being groomed for eventual leadership. He is reported to be fluent in English and the use of computers. The Washington Post reported that Saad was a key organizer of the May 12, 2003, al Qaeda bombing in Riyadh, Saudi Arabia. There have been reports that he is hiding along the Afghanistan-Pakistan border; others say that he is in Iran close to the Afghanistan border, in a region not controlled by the Iranian government. The Arab newspaper Asharq Al Awsat says that Saad is now one of the principal leaders of al Qaeda, but I'm skeptical of that. Al Qaeda is too sophisticated to let such a young and inexperienced person take over. But he likely has an extremely useful talent: sounding like his dad.

I like to consider myself an expert in the voices of my wife and my two daughters. I notice them even in a crowded and noisy room. When one of them telephones me, I instantly recognize her -- but often incorrectly. The one I name is the one I expect, not the one who called. (They find this very amusing.) I don't know if the similarity of their voices is genetic or learned, but I know that others have similar problems. Parents and children tend to sound alike, and that effect is exaggerated when bandwidth is poor, such as in a telephone call or on a cassette recording. In fact, commercial speech recognition software that is "trained" to respond to a particular person's voice often will have a hard time distinguishing the voice of a family member. The more sophisticated systems that intelligence agencies presumably use may of course be less prone to such confusion -- but I suspect that this vulnerability to child and sibling spoofing remains. And I doubt that the U.S. government has a recording of Saad to use for comparison.

[via Follow Me Here]

Muller's conclusion is surprising, at least to me, but a very interesting one. If he's right, than obviously the people putting out the tapes can continue to produce and release them indefintely, but I wonder how long tapes of "Osama" can be accepted as authentic by his followers without their actually seeing the real thing? Surely there must be some point when they begin to get suspicious that they aren't being presented with any kind of picture of their leader? That time may be delayed by their desire to believe in Osama's continued existence, but I don't believe it can be held off forever.