When Neil Armstrong and Buzz Aldrin landed on the moon on 20 July 1969, Nasa used two film cameramen at mission control in Houston to capture the moment back on Earth. The footage has been regularly seen in the decades since but it has always lacked a synchronised soundtrack, which never made it into the archive with the film.

Now film maker and Apollo aficionado Stephen Slater, working with London-based archive film company Footagevault, has painstakingly united the visual material with high-quality recordings of the original mission audio.

Footagevault, which sourced and supplied the archive material for the award-winning documentary film In the Shadow of the Moon, started this process with the film's editor David Fairhead back in 2006, but only attempted to lip-sync a few seconds of footage.

Slater has taken it to a new level, synchronising more than eight minutes of the Apollo 11 landing. "Some of this footage has become almost as iconic as the shots of the Saturn V launching, or the Earth rising over the moon," says Slater. "But as a film maker I was always rather disappointed with the way the mission control shots were used in such a generic fashion, without any sense that it was the actual moment that the Eagle had landed."

By adding sound, Slater believed he could give the footage a stronger documentary feel, as if the viewer were experiencing the history for themselves.

Inspired by what had been done for In the Shadow of the Moon, Slater was convinced he could achieve a lot more, and started to look for a more systematic way of synchronising the sound. He soon noticed that the mission control clock, inadvertently captured in many shots, could be used as a reference point for his work.

"It displays the so-called Ground Elapsed Time or GET," he explains, "which is also logged against the air-to-ground flight loop sound recordings on the Apollo Flight Journal. I was then able to narrow down my search to maybe a few lines of dialogue, particularly if a shot showing the clock was featured close to a potential synchronisation point. It was then a case of trial and error, seeing which pieces of sync worked with which pictures."

Slater also used a view of the entire room captured from an overhead TV camera that filmed mission control during the entire descent and landing, and which most of the world would have seen when watching the live coverage on that July day. Although of inferior quality to the film archive, it allowed Slater to see where the two cameramen were standing and whether their positions and shots matched the film footage.

The cameramen were Jerry Bray and Bob Bird. Bray positioned himself at the front of the room near the Capcom (capsule communicator) console to capture Charlie Duke's conversation with the astronauts, while Bird stationed himself at the back of the room filming the reactions of Nasa's top brass, including George Low, Bob Gilruth and Chris Kraft.

After much trial and error, Slater managed to find a number of definite synchronisation points from the film rolls of both cameras, and so for the first time we can now say exactly when this historic footage was captured. His work has brought to life a few of the most well known pieces of mission audio.

"For example we can now see flight director Gene Kranz giving his controllers a 'Go' for landing," explains Slater, "and Charlie Duke saying 'We copy you down Eagle' in response to Buzz Aldrin's 'Contact light'."

"There is also visible frustration and tension on the faces of Duke and his fellow controllers during a period early on in the descent when Mission Control had lost communication with the spacecraft, a moment which the restored audio has now really brought to life."

"Sadly, the downside of finally matching this footage correctly with the audio is that it's become clear how many important mission control moments weren't captured on film," adds Slater. "Charlie Duke's historic line immediately following Neil Armstrong's 'The Eagle has landed' ... 'Roger Tranquility we copy you on the ground ... you got a bunch of guys about to turn blue, we're breathing again thanks a lot' is missing.

It appears that cameraman Bray simply stopped filming and turned away to record a different shot at this historic moment, unaware he was missing what must have been a priceless reaction from Apollo 11's key man on the ground."

Slater's historic handiwork can be seen at http://www.footagevault.com/project-mocr-apollo-11

Christopher Riley is the author of the Haynes guide Apollo 11: Owners' Workshop Manual. He curates the online film archive at Footagevault.com.