When did the creation process for Godzilla's menacing roar begin? Supervising sound editors and designers Erik Aadahl and Ethan Van der Ryn say they were brought on to Godzilla by director Gareth Edwards and Legendary Pictures CEO Thomas Tull to start thinking about the title creature’s iconic roar at an unusually early time, even before the film had gotten the green light.

Van der Ryn won Oscars for The Lord of the Rings: The Two Towers and King Kong and has three additional nominations, including for Argo and Transfromers: Dark of the Moon, both of which he shared with Aadahl. But this experienced team knew that creating Godzilla’s distinctive roar for the Warner Bros. release would be a challenging undertaking.

STORY: 'Godzilla': What the Critics Are Saying

"[Edwards and Tull] are huge Godzilla fans -- actually Thomas’ office has Godzilla sculptures," Aadahl tells The Hollywood Reporter. "Seeing the fans that they were and recognizing that the original roar was such a famous and iconic sound, we felt it was important to pay homage to that. Not do something completely different but to embrace the template of the original, and at the some time update it with the technology that we now have."

They started by going back to Ishiro Honda’s classic 1954 film. "The original music composer, Akira Ifukube, came up with the idea of using a musical approach to create that reptilian sound," Aadahl explains. "It was a double base; they used a leather glove with pine tar around it to rub against the strings to get that vibration that we all know. That eeeee-rrr.

"We dissected that original roar and figured out exactly which key musically it was in, which is a C to D on the piano, and the finishing bellow that has the same notes on a lower octave. We figured out the timing, cadence and musical pitch of that original roar, and then started to experiment with different ways to re-create it."

Adds Van der Ryn: "We bought a microphone that was able to record above the range of human hearing. We started experimenting will all different types of sounds -- sounds that we couldn't actually hear when we were recording. But when we slowed them down into the human range of perception, we had an incredible palette of normally invisible sounds that people normally don't get to hear."

For six months, the pair conducted hundreds of experiments, recording everything from a rusty car door on a 1972 Plymouth to a squeaky coat hanger. They also experimented with Ifukube's technique. "We got a double bass and used all types of ways of getting friction on the string," Aadahl says. "The one that yielded the closest sound to the original was using a climbing boot with plastic soles. But we wanted to keep experimenting."

PHOTOS: Godzilla Over the Decades

In the end, the main shriek came from one sound, a "non-living thing," which the sound pros and Edwards have decided to keep a secret -- at least for now -- effectively taking a cue from renowned sound designer Ben Burtt, who didn't initially reveal that E.T's voice was actually an elderly woman who was a heavy smoker. Says Aadahl: "They didn’t tell the public until way after the movie came out because they were afraid audiences would be thinking about this lady when they should be thinking about E.T."

While working on the film, the pair did quite a bit of recording on the Warner Bros. backlot. "We pumped out all the designed creatures sounds [through the Rolling Stone tour speaker array] and rerecorded them from across the lot, from rooftops, from inside cars, to create realism," Aadahl says, adding that the sound clearly traveled. "We got phone calls from Universal Studios; the tour groups were asking about 'weird sounds.'"

Rerecording mixers Tim LeBlanc (dialogue), Gregg Landaker (FX) and Rick Kline (music) then mixed the film on Stage 10 at Warner Bros.

This included a version for Dolby’s immersive Atmos sound format that places speakers around an auditorium and even across the ceiling. "Atmos was pretty awesome for this film," Aadahl says. "In this movie it’s all about the spatial quality and the reflections of the creature vocals in the environments. And there’s also flying creatures, so using the ceiling is huge. I would love for everyone to see it in Atmos; it’s a whole other dimension."

The work of Van der Ryn and Aadahl -- who operate using the moniker E2 -- will next be heard in Michael Bay’s upcoming Transformers: Age of Extinction.

Email: Carolyn.Gairdina@THR.com

Twitter: @CGinLA