Few sound effects in film are as iconic as Godzilla’s roar. So the task of updating it for Gareth Edwards’ reboot of the monster franchise was nothing short of daunting.

For starters, there were 60 years of history to contend with. “It’s kind of a part of our culture — Godzilla and his roar,” says Erik Aadahl, sound designer on the film, which topped the box office last weekend. “It’s one of those sounds where you can go anywhere in the world and everybody knows what it is. It comes with a lot of responsibility to redesign it. Our starting point really was wanting to embrace the original and pay homage to it.”

So Aadahl and fellow Godzilla sound designer Ethan Van der Ryn went back to the very beginning. As the legend goes, the team designing the original roar for the first Godzilla film in 1954 tried recording animal sounds, but were unhappy with the results. It wasn’t until the film’s composer, Akira Ifukube, suggested using a musical instrument that they reached their eureka moment: They coated a leather glove with pine tar resin (to create friction) and rubbed the glove down the strings of a double bass, resulting in that classic “aaaAAAAaaaa” shriek.

Aadahl and Van der Ryn embarked on a similar process of experimentation. They also tried animal sounds, and even reproduced the glove-on-strings test, “but it still didn’t feel right,” Aadahl admits. The pair spent six months over a three-year period trying to perfect the roar, and finally found a scream worthy of the King of the Monsters with the aid of new technology, including scientific microphones that record above the range of human hearing.

“We recorded these [inaudible] sounds and then we would bring them back into the studio and slow them down, pitch them down, and bring them into the range of human hearing,” Van der Ryn explains. “That was really an exciting thing for us because it allowed us to exploit this vast power of unexplored sounds.”

But the team couldn’t just use a cry that sounded intimidating or cool. They were creating the voice of their main character, after all.

“As we were working on the roar we kind of broke it down into two parts: the initial shriek and the finishing bellow,” Aadahl says. “To me, both parts have different emotional reactions: The initial is the fury of nature and the finish is this knowing, this understanding that conveys a deeper, richer soul. And ultimately, when you give voice to something, you are giving it its soul. So, we’ve become very protective over our big beast because of that.”

So protective, in fact, the pair refuses to spill what technique they used for the final product. They didn’t even tell director Edwards how they created it until after the film was complete. “It’s kind of like a magic trick, and a magician doesn’t tell the audience, ‘OK, here’s how the trick is done,'” Aadahl says. “It kind of ruins the trick. You want this suspension of disbelief.”

He would, however, divulge a few things that didn’t work: rubbing the palm of their hands against the surface of a drum; pulling out the squeaky legs of an ironing board; opening old, rusty car doors that would groan and wail.

But there’s one thing that absolutely remains the same from the original: the musical key and cadence of the roar. “If musicians listen, they’ll hear that we go from a C on the piano to a D on the piano, musically, which is what one of the iterations of our favorite roar did as well,” Aadahl reveals.

After approximately 50 versions, here’s what 2014 Godzilla sounds like:

The experience, of course, is even more powerful in the moment, and particularly in theaters. Godzilla was mixed using Dolby Atmos, a new frontier in sound technology that allows engineers to deliver explosions and giant footsteps and roars from every part of the room — even overhead, which might cause audiences to inadvertently duck when a MUTO launches an aerial assault.

“Where before Atmos we were restricted to one plane that you might call the X-Y axis, with Atmos, we have this whole vertical component,” Aadahl explains. “The Z axis is introduced. It kind of pulls the curtain away in terms of spacial-ness, and the audience can now be immersed in this hemisphere of sound.”

And why wouldn’t you want to hear that kaiju chaos from all possible angles?

“So much of the power of the roar, as well as the vocals of the other creatures, comes not just from the sound itself but from how the sound affects the environment that it’s taking place within,” Van der Ryn says. “And with Atmos, we’re able to use all the speakers in the room to help describe that environment and the geography of the space.”

Getting the realness of the sounds for Godzilla was so important to Aadahl and Van der Ryn, they took their roar for a test run on a back lot at Warner Bros.

“We actually ended up renting the tour speaker array for the Rolling Stones, which was about 10-feet tall and about 18-feet wide,” Van der Ryn says. “So we played all the creature vocals through that and then recorded it through cars, from the other side of the lot, from rooftops, from within storefronts, so we could get that real-world feeling of what it would be like to be on a city street and have Godzilla 50 feet away just doing his roar.”

For this “worldizing” experiment, the crew had to send flyers to surrounding communities warning neighbors of the potential sound disruption. Despite those preemptive measures, “Burbank P.D. started getting calls, people were tweeting, ‘Godzilla’s at my apartment door!'” Aadahl recalls. They even got calls from Universal Studios across town “because tour groups were asking, ‘What the heck’s going on down in the valley?'”

By their estimates, the roar traveled roughly three miles. But what if Godzilla were real? Based on their experiments, could Aadahl and Van der Ryn guess how far away the monster’s cry might actually be heard?

“We judged the speaker array size roughly off the girth of what Godzilla’s jaw would have been, which is about the size of a city street,” Aadahl says. “Godzilla’s quite tall, so if we had had our speaker array another 300 feet up in the air, I think it could have traveled beyond three miles.”

“It might have doubled the distance,” Van der Ryn says.

To hear how Aadahl and Van der Ryn’s roar compares to the calls of Godzillas past, check out the timeline in the video below:

And for more background on the roar, an interview with Aadahl, Edwards, and Godzilla producer Thomas Tull is below:

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