To help bring a film like Rogue One — which takes place in far-off worlds with ships and creatures we've never seen before — to life, sound designers will often use unexpected sound effects that are warped and manipulated, until you can't imagine a droid like K-2SO sounding any other way.
Sound On Sound magazine visited Skywalker Sound and interviewed the sound designers and foley artists that worked on Rogue One: A Star Wars Story, who revealed some interesting secrets about how they sourced some of the sound effects used in the movie.
In the case of K-2SO, a security droid working for the Galactic Empire that was reprogrammed to serve the Rebel Alliance, supervising sound editor Christopher Scarabosio wanted to create a unique sound for the droid's movements to help enhance the character voiced and performed by Alan Tudyk. He initially recorded the sounds of the motors that powered his standing desk, but soon realised they made K-2SO sound exactly like Iron Man, which is something the sound designers wanted to avoid given the film takes place in an entirely different galaxy to Tony Stark's.
Scarabosio still used the sounds from an electric motor to accentuate K-2SO's movements, but recorded from the powered mechanisms that automatically open and close doors for those with limited abilities. Even though K-2SO is one of countless droids inhabiting the Star Wars universe, by putting extra care and originality into the character's sound effects, it helped make the emotionless robot feel more lifelike.
For scenes taking place in the Holy City on Jedha, a place full of bustling markets and temples, Scarabosio had originally included a recording of a call to prayer in the multiple layers of noise and din that were designed to bring the crowded city to life.
There were concerns about using the recording in the movie, however, so sound designer David Acord came up with an alternative. He recorded himself singing the fight song for the Philadelphia Eagles football team in a different language, which ended up sounding like a unique call to prayer on an alien world. It also lets Acord boast that he's the biggest Philadelphia Eagles fan in our galaxy, as well as one far, far away.