TWO years ago, Nissan hired the studio Man Made Music for what seemed like a straightforward task: Design a sound that its quiet electric vehicles could play to announce themselves on the road.
The automaker wasn't just splurging on a flashy feature. It was preparing for a federal regulation set to take effect next year that would require all hybrid and electric vehicles, which are quieter than their gas-guzzling ancestors, to emit noise at certain speeds for pedestrian safety.
This week, the agency that oversees the rule, the National Highway Traffic Safety Administration, proposed changing it to let automakers offer drivers a suite of sounds.
For now, though, Nissan plans to include just one with its electric Leaf next year: Canto, a resonant hum created by Man Made Music whose pitch rises as the car accelerates.
Designing such sounds is a complex undertaking, according to Joel Beckerman, the founder of Man Made Music.
With Canto, the team had to address safety and maintain a brand identity, all in a three-second loop that is distinctive yet doesn't stand out.
"If we do our job in this kind of situation, then you don't notice what we did at all," Beckerman said. "It just becomes natural, it's just a part of your life, it's a part of your environment. When you get it wrong, that's when people notice."
The team at Man Made Music, which is used to developing audio for TV, movies and radio, spent nearly half of 2017 working on the sound, a layering of sampled wind and string instruments, and analog and digital synth sounds.
"A surprising element we found ourselves relying on were pure 'sine waves' from analog synthesisers," Danni Venne, the studio's creative director on the Nissan project, said in an email.
"We also found that adding bits of 'white noise' to the mix gave us a lot of control to shape and colour the sound. It's almost like we built Canto from fundamental building blocks of sound."
While the advent of quieter hybrid and electric vehicles presents an opportunity to build such sounds from scratch, there is a long history of sound design in the automotive industry.
Muscle cars have their distinctive throaty growl. Harley Davidson motorcycles have that syncopated "potato-potato-potato" chug. (That's really what they've called it.)
There is also a history of maintaining zombie sounds long after technology has made them obsolete. On smartphones, for example, the actions of locking the device or taking photos are often accompanied by the noises of a mechanical lock or camera shutter.
In financial apps, transactions are often accompanied by the sound of jingling coins or a cash register.
In the case of hybrid and electric vehicles, though, the need for sound is about more than the user experience: It's about safety.
About a decade ago, the National Highway Traffic Safety Administration found that hybrid electric vehicles were 35 per cent more likely than those with internal combustion engines to be involved in a pedestrian accident.
Hybrids were also 57 per cent more likely to be involved in accidents involving bicycles.
In 2010, Congress passed a law to enhance pedestrian safety, instructing the agency to craft a rule mandating that hybrid and electric vehicles emit noise.
The rule was finalised in 2016 and requires that such noises be produced when the car is driving at speeds up to 30 kilometers per hour (not quite 19 mph).
Above that, tire, wind and other noises were warning enough, it deemed. The move was celebrated by the blind community.
Automakers requested a few changes, though, including allowing owners to choose from a range of sounds rather than just one.
On Tuesday, the agency proposed making that tweak, and said that it would accept input on the move until November.
Regulators around the world have been imposing or weighing such requirements. In the European Union, for example, one such rule just took effect in July.
As a result, major carmakers have been working on crafting sounds to meet those requirements.
Jaguar, for example, said it worked for four years on the futuristic noise for its I-PACE SUV.
For the 2020 model of the Chevrolet Bolt, General Motors designed the vehicle's sound in-house, using a quiet electric whirring as a starting point, according to Todd Bruder, the engineer who led development of the sound. NYTIMES