IRCAM’s Renault sounds were, indeed, surprisingly mellow, although perhaps less like birdsong than like a washing machine set to the delicates cycle. The Parisian soundscape will surely benefit from them. But would anyone hear these élégantes French alerts in New York, particularly over the bedlam and blare of all the gas-powered vehicles in its traffic-clogged streets?
An automobile powered by internal combustion makes a racket. The induction of air, its compression inside the piston sleeves, the explosion of the vaporized gasoline, and the expulsion of CO2 exhaust (“suck, squeeze, bang, and blow,” in car talk) produce loud, low-frequency reports, rumbles, and vibrations.
At General Motors, engineers in the Noise and Vibration Center are responsible for fine-tuning that din. Douglas Moore, a senior expert in exterior noise at G.M., started working at the company in 1984, when he was still an undergraduate at Michigan State. He has spent all but eight years of his career with G.M., where his job, and that of his Noise and Vibration colleagues, has been to silence, dampen, and modulate the sounds made by internal combustion, depending on the brand. Traditionally, when tuning a Cadillac, Moore and his colleagues would try to make the engine as quiet as possible, because quiet signifies luxury to the classic Cadillac buyer. In tuning a Corvette, Chevrolet’s “muscle car,” on the other hand, the engineers want some of the bang-bang-bang of internal combustion to come through, because that conveys power to the driver.
The engine’s sound isn’t the only thing that the engineers work on. Many prospective buyers’ first experience of a car or a truck is the CLICK ker-CHUNK that the driver’s-side door makes when they close it, followed by a faint harmonic shiver given off by the vehicle’s metal skin. The door’s weight, latches, and seals are carefully calibrated to create a psychoacoustic experience that conveys comfort, safety, and manufacturing expertise.
In designing electric versions of popular brands, U.S. automakers have to decide whether to make the E.V.s mimic their gas-driven counterparts or whether, like Renault, to divert from the familiar sound. The Passenger Safety Enhancement Act directives allow automakers to craft their own branded alerts, so long as they meet certain specifications.
Moore’s first E.V. project was the 2012 Chevy Volt, which emitted a pedestrian alert years before the law required one—a vacuum-cleaner-like hum that increased in frequency as the car sped up. “I have new colors to paint with,” Moore said. “Instead of a palette of internal-combustion sounds, I have a palette of AVAS sounds. But it’s the same approach. Now, instead of generating them with the physical components of the car, which has its pros and cons, we’re generating them electronically.”
Moore is also the longtime chair of a group within the Society of Automotive Engineers called the Light Vehicle Exterior Sound Level Standards Committee, which helps develop tests that regulators use to measure safety on the road in the U.S. His group led the investigation into developing minimum-sound standards for E.V.s and hybrids, and establishing parameters to govern the decibel level, pitch, and morphology of the warning signals. Moore once came to the N.F.B. headquarters and tried navigating in traffic when blindfolded. His N.F.B. instructor was impressed that the engineer could identify a 2005 Chevrolet Camaro and a 2009 Cadillac Escalade by their distinctive engine sounds.
Moore explained the S.A.E.’s relationship with federal highway-safety regulators by saying, “We figure out how to measure things. N.H.T.S.A. says how much.” I asked Moore why the regulations don’t require that E.V.s more closely resemble I.C.E. vehicles, since, as the N.F.B.’s John Paré had noted to me, we’re already used to those noises. Moore replied, “The purpose of this sound is to provide information about what the vehicle is doing. And there’s more than one way to provide that.” He paused. “Yes, we’ve learned internal-combustion sounds over a hundred years,” he continued. “But before cars were around we knew that the clip-clop of horses meant the wagon was coming. So, there’s nothing inherent in those engine sounds.”
A well-designed alert reaches the people who need to hear it, without annoying those who don’t. To thread this sonic needle, engineers can vary a particular sound’s decibel level, which indicates the volume of air pressure that the sound waves displace, and they can also adjust the sound’s pitch, or frequency. Both decibel level and pitch determine the intrusiveness of that sound. The danger is that you create a sound that cries wolf, as it were: it works at first, but after a while people tune it out, so you have to pump up the volume.
Although humans are capable of hearing frequencies between twenty and twenty thousand hertz, we hear in “octave bands,” in which the highest frequency is double the lowest one. (In a musical C octave, the high C is twice the frequency of the low C.) The regulations specify that AVAS sounds must cover four separate, nonadjacent octave bands. A so-called broadband sound of this type, such as the staticky squawk that Amazon delivery vans recently began making when reversing, is less piercing, more robust, and easier for the hearer to locate directionally than an alert that occupies a narrow frequency range, such as the back-up beepers on Con Ed trucks. Not incidentally, the nonadjacent-octave-band rule precludes using a musical phrase as an alert—the pitch-shifting would sound awful—as well as any vocal alerts, human or animal. How would the blind tell the street from the sidewalk if electric cars spoke or barked?
By permitting automakers the latitude to brand their alerts, the N.H.T.S.A. rules have created a new design form: acoustic automobile styling. Pedestrians and cyclists won’t just hear the vehicle coming; they’ll know what kind of car it is. For acoustic designers, both the pedestrian alerts of E.V.s and their rich in-cabin menus of sonic information represent the dawn of a new age. “I feel fortunate that I get to work on features that will influence the way the world will sound,” Jigar Kapadia, the creative-sound director for General Motors, told me.
Kapadia, who studied electronics and telecommunications engineering at Mumbai University and has a master’s in music technology from N.Y.U., collaborates with Moore and others at G.M.’s sound lab in Milford, Michigan. For each sound, the team comes up with about two hundred variations and then tests them on their colleagues in the jury room, until they have arrived at a few finalists they can road test on vehicles.
Kapadia likens an alert-system sound to a perfume. “Just like a perfume, it unfolds,” he told me. “The alert has a base note, a middle note, and a top note.” He added, “These layers are amalgamated together to bring out a cohesive organic sound, or a futuristic sound, based on what kind of brand we are focussing on.” He noted that the pedestrian alert on the 2023 Cadillac Lyriq, the first electric version of G.M.’s long-standing luxury car, was made with a didgeridoo, an ancient Australian wind instrument that is based on the musical interval known as a perfect fifth. However, for G.M.’s nine-thousand-pound electric Hummer, which recently went on sale, Kapadia said, “we wanted a more distorted sound.” He paused, and then added, “A bold Hummer sound.” The Hummer’s forward-motion alert made me think of church, when the organist launches into the next hymn. The back-up sound is something like its dystopian twin.
At the Ford Motor Company, in order to find out what car buyers thought electric vehicles should sound like, engineers and consultants conducted “customer clinics” and launched a Facebook campaign. Judging from the number of responses, Ford fans were keen to make their opinions known. My own survey, largely based on reading comments under YouTube videos of various branded E.V. sounds, is that most people think that E.V.s should not resemble I.C.E. cars. Higher frequencies are thought to signify clean energy and software-driven intelligence; E.V.s ought to whoosh and zoom like the flying personal vehicles of science-fiction films such as “The Fifth Element,” “Gattaca,” “Blade Runner,” and, of course, “Star Wars.” In many cases, in fact, Foley artists created those futuristic vehicles’ sound effects from recorded I.C.E. noise. In Ridley Scott’s “Blade Runner 2049,” the twist is that Ryan Gosling’s flying vehicle sounds like a broken-down I.C.E. jalopy.