The biggest hurdle would be mimicking the cadence and rhythm of human speech. Synchronizing a doctored soundtrack with existing video would also be tough, and technology that can synthesize Arabic speech is still in its infancy.
Chi-Lin Shih, a language modeling scientist at Lucent Technologies' Bell Labs, described the process as akin to reassembling a broken vase by gluing together its shards. Close scrutiny would likely reveal the cracks.
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Software tools allow for elements of a person's speech to be glued together to put words in their mouths, but such a doctored recording would not sound natural to an expert listener, said Kenneth Stevens, head of the speech research lab at the Massachusetts Institute of Technology.
President Bush called the charge preposterous. Administration officials said they intentionally declined to try to enhance the video's sound or picture so as not to give detractors ammunition.
The videotape, which has been widely seen in the United States, was distributed Friday to Arabic media along with an Arabic transcript so people who speak Arabic can watch it in the original language with the subtitles and the sound in Arabic, said State Department spokesman Richard Boucher.
The creators of AT&T's Natural Voices software, for example, claim the program can mimic the speech of actors now dead, such as John Wayne. By allowing computers to analyze enough tapes of an actor's voice, the program could synthesize the voice, allowing it to make statements Wayne never said.
Theoretically, the same could be done with bin Laden's voice since recordings of his speech are readily available, said Lynn Shepherd, a vice president of Fonix Corp., a speech synthesis software company in Salt Lake City.
If they had a lot of recordings of bin Laden, they could create some speech that sounded pretty good, Shepherd said Friday.
However, most software requires a dozen or more hours of high-quality studio recordings, where a speaker is asked to make all of a language's particular combinations of sounds.
It takes engineers months to break down all these voice fragments so that I can reproduce the language, said Bill DeStefanis, who heads speech technology for ScanSoft Inc. of Peabody, Mass.
The idea that the U.S. government could have done this in the space of a month is highly improbable, DeStefanis said. With a short snippet, I might be able to fake you out, but not a long speech.
On the tape, some of bin Laden's words are unintelligible. The tape's poor sound quality ould theoretically be used to mask tampering, experts said. But beyond synthesizing a voice, doctored speech would have to be synchronized video - another difficult task usually easy to spot.
Digital synchronization of sound and images is a staple of Hollywood filmmaking. In the 2000 movie Gladiator, actor Oliver Reed died before shooting ended and the filmmakers pieced together several scenes using previously shot footage.
DeStefanis and others said, however, that fooling the trained eye is difficult. The human eye and ear are very good at seeing out-of-synch lips, he said.
Also, few if any of today's sophisticated speech synthesis engines have been programmed to generate bin Laden's native Arabic, Shepherd said.
There are some low quality ones, but nothing that would be good enough, Shepherd said.
As for reaction to the tape, among Americans and their allies, bin Laden's satisfied and knowing musings about the Sept. 11 attacks hardened attitudes already set in stone.
In the video shown to the world, bin Laden acknowledged his advance knowledge of the suicide hijackings and spoke about how the destruction had exceeded even his "optimistic" calculations.
U.S. legal experts called the tape devastating, a "virtual confession," in the words of one.
However, newspapers in the Arab world Friday played down the bin Laden videotape. Most Friday papers were dominated by the Israeli-Palestinian conflict.
In Friday prayer sermons, a traditional indicator of national sentiment in the Middle East, mosque preachers did not speak of the tape. Instead, they focused on religion the day was the last Friday sabbath in the holy month of Ramadan.
The few Arab officials and analysts who commented on the tape accepted it as damning evidence that the Saudi-born Islamist dissident was behind the attacks which killed nearly 3,300 people.
President Bush, however, said anyone questioning the tape's authenticity is reaching for a feeble excuse to support him.
"I mean, this is bin Laden unedited," Mr. Bush said Friday. "It's preposterous for anybody to think that this tape is doctored.
"That's just a feeble excuse to provide weak support for an incredibly evil man."
The president accused bin Laden of being so cold hearted that he laughed at those he sent to die, reports CBS News White House Correspondent Bill Plante, and he scorned bin Laden as a coward in hiding.
"We're chasing a person obviously who is willing to send suicide bombers, on the one hand, and hide in a cave," he said. "Somebody who...encourages young people to go kill themselves, and he, himself, refuses to stand and fight."
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