Buzz Aldrin poses on the Moon, allowing Neil Armstrong to photograph both of them using the visor reflection. New evidence reveals that Armstrong's famous landing speech began: "That's one small step for a man".

Credit: NASA

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WASHINGTON DC: An Australian researcher using high-tech software has revealed what Neil Armstrong really said as he became the first human to step onto the Moon's surface.

"That's one small step for man, one giant leap for mankind," said Armstrong on 20 July 1969, in a transmission heard around the world, 386,232 kilometres away.

But Armstrong has always insisted he intended to say, "That's one small step for a man, one giant leap for mankind," and he and the U.S. space agency NASA have maintained that he said the "a".

For the 37 years since the Moon landing, official documents have reflected uncertainty, some saying "for man," others "for a man." Now Sydney researcher Peter Shann Ford says he has the technological proof that Armstrong said the critical "a" that gives the true meaning of humankind's first words on a heavenly body.

Armstrong's authorised biographer, James Hansen, a history professor at Auburn University in Alabama, said that Ford's analysis of the recorded transmission is "awfully persuasive to me." Hansen said he had been "highly skeptical" when the Australian researcher contacted him 10 days ago with his findings.

Ford had detected the errant "a" in data about 35 milliseconds long, pronounced so quickly by the Apollo 11 mission commander that it was in a "sub-aural region," Hansen said.

Armstrong's "voice register is without question in the electronic recording," the history professor said, noting the historical importance of having the misquoted message corrected.

Armstrong had "fully intended" to say the "a," but "Neil didn't know what happened to it," said the author of the 2005 biography First Man: The Life of Neil A. Armstrong. The new proof indicates "he said exactly what he intended to say," he added.

Hansen said the findings were made public last week after he, Armstrong, 76, and NASA officials presented the data at the Smithsonian Institution's Air and Space Museum in Washington, then at NASA headquarters. Armstrong was on holiday and not immediately available for comment.

The findings "looked promising" and "just backs up what we thought all along," NASA spokesman Grey Hautaluoma said. The professor said there "may be an even purer recorded transmission" at Parkes Observatory in Australia, which received the transmissions from the Apollo 11 Moon landing.

Ford's company, Control Bionics, specializes in nerve-controlled computing to overcome physical disabilities. Professor Stephen Hawking, author of the best-seller A Brief History of Time, is among the first people to test the company's technology, Hansen said.