Jeremy Hsu
May 31 · 12 min read
Much trickery goes into manipulating car sounds beyond films such as “Mad Max: Fury Road.” Credit: Warner Bros

Director George Miller and the filmmakers of “Mad Max: Fury Road” had a problem. They had emphasized practical visual effects by building and destroying dozens of vehicles during the 2015 film’s main action sequences: a long road chase and running battles with cars and trucks in a post-apocalyptic wasteland. But the audio recordings of the actual vehicle sounds seemed weak in comparison with the dazzling visual display of vehicular carnage.

To give the “Mad Max” vehicles a larger-than-life sound, Miller and his team turned to Hollywood sound designers for help. The sound designers added sound “cheats” and “sweeteners” — everything from animal roars to jet engine whines — based on a library of sound samples collected over several decades. The result is that the “Mad Max” War Rig, an 18-wheel semitrailer truck, has a husky engine sound backed by menacing bear roars. Roving packs of warriors on motorcycles emit wolf growls as they zoom past. Even the sound of bees is used to heighten the experience of seeing an attack by a swarm of spiky cars.

“Truthfully, anytime you go and record something in the real world, what you record is not super impressive unto itself nine times out of 10,” says Scott Hecker, a sound editor at Formosa Features. “Even though you have this bright, shiny new sound you just recorded, you still have to add other sounds to make it dramatically appealing to an audience.”

The work of Hecker and his colleagues paid off when “Mad Max: Fury Road” won Academy Awards in both major sound categories. But the careful crafting of vehicle sounds is not limited to Hollywood’s illusions of squealing tires and revving engines during cinematic car chases. The world’s largest automakers have spent decades on shaping the sound experience of drivers and passengers. Such real-life engineering of car sounds goes beyond the removal of annoying sounds; it can also include the artificial boosting of more pleasing sounds.

Car sounds matter because they have a huge, unappreciated influence on how people perceive a Hollywood film’s epic car chase or a highway drive in real life. Rather than taking a backseat, sound is frequently in the driver’s seat controlling the brain’s overall sensory perception of the world. Automakers have instinctively sensed the importance of car sounds since the dawn of the motor age more than a century ago, but the scientific research explaining why car sounds matter so much has only begun emerging in recent decades.

The Case of the Missing Lion’s Roar

Sports and luxury car brands provide one window into understanding the importance of car sounds. Car owners have grown accustomed to associating certain sounds with the power, speed and reliability of the respective car models. In turn, automakers have also emphasized their vehicle engine sounds as symbols of qualities related to “sportiness” or luxury. To satisfy customer expectations, some automakers take great pains to maintain such signature sounds even as car designs and technologies change over time.

For example, an accelerating Porsche sports car may subconsciously remind listeners of the power and force behind a lion’s roar or the trumpeting of an elephant, says Friedrich Blutner, a psychoacoustic researcher at Synotec Psychoinformatik in Germany. That signature sound first arose from the automaker’s choice to use air cooling for its combustion engines.

When Porsche switched back to water cooling, sports car enthusiasts grumbled about the missing air cooling sound. A journalist observed that the Porsche “lion” does not roar anymore. In response, the automaker artificially reintroduced the signature sound in its vehicles by playing audio of the air cooling sound through speakers.

People care about the missing “lion’s roar” because they have learned to associate the sounds of their beloved Porsche with the qualities of a certain car brand. Those qualities may include a sense of sportiness or luxury when driving or riding in a particular car. But many people may not quite realize how sounds affect their perception of the overall car experience until those sounds change.

“Engine sounds set expectations and also act as a signature sound associated with a particular make,” says Charles Spence, an experimental psychologist and head of the Crossmodal Research Laboratory at the University of Oxford in the UK. “If you pay a lot of money for specific car brand, you want it to sound different from other cheaper brands.”

Human brains have the basic neural and perceptual capabilities to perceive sensory information such as the sounds and visual images of cars, says Souta Hidaka, a perceptual and cognitive psychologist at Rikkyo University in Japan. But babies do not emerge from the womb with the knowledge that certain engine sounds mean a Porsche driver is putting the pedal to the metal. Instead, humans gradually appreciate the relationships between different types of sensory information through experiences learned after birth.

Illusions of Sound and Vision

The human brain frequently combines sensory information received from two or more sensory signals that originate from the same source, says Ladan Shams, a cognitive psychologist and director of the Multisensory Perception Lab at the University of California, Los Angeles. The brain tends to give more weight to what it perceives as the most reliable sense. Sometimes that means sound can have a greater influence than sight in the perception of moving objects such as cars.

“Perception of the world is like a democratic process, where each sensory modality casts a vote and all votes are taken into account, but the difference with our political system is that in the brain, not all votes are given the same weight or are counted equally,” Shams says.

In 2010, Hidaka and his colleagues published a study in the journal PLOS ONE that showed how learned experiences can lead the brain to put more weight on sound than sight in perceiving visual motion. They first placed two circles side by side and alternately flashed their images to give the appearance of horizontal motion. Each circle’s appearance was accompanied by a sound tone of a specific and unique frequency, so that study participant’s brains eventually associated the different tones with the apparent horizontal motion of the circles.

When the researchers continued to play the different sound tones but only flashed the circle in a single fixed location, the study participants still perceived the circle as moving horizontally. That effect of sound tricking the brain into seeing visual motion lasted for at least a few days.

Several studies have also shown how engine sounds can influence people’s perceptions of cars in motion. In 2008, researchers at the University of Queensland in Australia published a paper in the journal Perception that showed the loudness of car engine sounds affected how people perceived the speed of a traveling car. As study participants watched video clips of cars in motion, they reported slower speeds for video clips accompanied by engine sounds five decibels lower (softer) than the “normal” engine sounds.

Race car sounds changed when Formula One switched from V8 to V6 engines. Credit: Formula One

Engine sounds matter as automakers have begun moving away from muscular eight-cylinder V8 engines toward smaller, quieter engines with fewer cylinders. Austrian researchers found that people perceive the sound of two-cylinder engines as having half the perceived engine speed of a four-cylinder engine — even if both engines operate at the same speed.

That can lead drivers to waste fuel because they underestimate the speeds of two-cylinder engines and do not shift into higher gear until later than they should. Such research by the automotive consulting firm AVL and the Institute of Electronic Music and Acoustics, University of Music and Performing Arts Graz in Austria was detailed in the 2016 book “Automotive NVH Technology.”

Rise of Masculine Sound Culture

People usually remain unaware of how engine sounds subconsciously affect their perception of car speed. But they do notice when signature car sounds have changed. In 2014, Formula 1 regulations made the organization’s race cars change from V8 engines to a V6 engines. The switch meant a quieter sound in the “human scream” frequency range for the race cars, which led some fans to complain about the loss of the old engine’s “scream,” says Trevor Cox, professor of acoustic engineering at the University of Salford in the UK.

The Ford Motor Company confronted a similar sound problem. The U.S. car manufacturer’s iconic Mustang sports car traditionally offers a powerful V8 (eight cylinder) engine in its most expensive models. But in 2014, Ford began offering less expensive Mustang models with either a V6 engine or a turbocharged “EcoBoost” engine with just four cylinders. To compensate for the loss of the V8 sound, the EcoBoost model used a system called active noise control to monitor the sounds that the driver hears and amplify certain “instruments and notes” of the car engine while canceling undesirable sounds.

“The team ultimately decided on a sound that is athletic and youthful to accompany the nimbler platform of the all-new Mustang,” according to a Ford press release. “At the same time, the Mustang EcoBoost has a traditional American feel, emitting a low-frequency sense of powerfulness that is a subtle reminder of the DNA it shares with the V6 and V8 Mustangs.”

Even the most muscular examples of modern sports cars have an incredibly refined sound compared with the noise barrage of their ancestors. Before the 1920s, cars represented the toys of wealthy aristocrats and sportsmen who reveled in their noisy vehicles as status symbols.

“It was great for the car owners when the vehicles made a lot of noise, because that really underlined the masculinity of the car,” says Karin Bijsterveld, historian and professor of Science, Technology & Modern Culture at Maastricht University in the Netherlands. “You were arriving and everyone could hear it.”

Loud combustion engine cars stood in stark contrast with electric cars at the dawn of the automobile age. Such early electric vehicles seemed to have the selling advantage of being fairly noiseless. But advocates of the combustion engine vehicles counterattacked by criticizing the electric vehicles as “feminine,” writes Gijs Moms, a historian at Eindhoven University of Technology in the Netherlands, in an article titled “Orchestrating Automobile Comfort” published in the 2 April 2014 issue of the journal Technology and Culture.

Electric cars had mostly vanished by the late 1920s and 1930s, not to be seen again in significant numbers until their more modern renaissance. But their silent competition had forced automakers to begin taking the noise issue seriously for the sake of comfort. Together, automakers and customers defined a “masculine car culture in which the car was implicitly defined as adventurous to the senses, but in a civilized way,” Moms writes.

Engineering the Sound of Silence

Many standards for car sounds began to change in the 1920s and 1930s, says Bijsterveld at Maastricht University. The growing popularity of car radios in the 1920s began changing people’s expectations about the competing noise coming from cars. Automakers also wanted to sell people on the idea of closed family cars for touring around the country.

As a result, automakers began thinking of ways to create a more comfortable, trustworthy ride by reducing physical vibrations and dialing down the volume of annoying sounds. Car engineers began to figure out ways to dampen or silence unwanted noises involving the car engine, onrushing wind, tinny car doors and squeaking suspensions.

Credit: The Design Council/The Manchester Metropolitan University

New advertisements played their part in shaping customer expectations for quieter cars. One 1929 ad compares a smooth car ride with a cinematic experience of seeing the landscape roll past the car windows. Automakers also promoted the idea of silence as being suitable for the “civilized ear” and as a foundation for luxury car experiences. A different Rolls-Royce ad shows a chauffeured car with the marketing slogan “As silent as its shadow.”

A “quiet” car’s noise level in the first half of the 20th century would still likely drive most modern drivers crazy. In the 1930s, American families tolerated cars that sounded louder than a large orchestra when reaching speeds of 60 miles per hour. Even cars from the 1960s or 1970s may still sound loud compared with modern standards. “If someone drove a 1970s car now, they’d probably think it was noisy and badly engineered,” says Cox at the University of Salford.

Ordinary people can identify 20 to 30 car sounds that don’t necessarily inspire confidence: sounds such as “rattling, knocking, blaring, quacking, and stuttering,” says Blutner at Synotec Psychoinformatik. Today, car engineers use extensive “sound cleaning” techniques to remove such sounds from modern car designs.

The modern resurgence of quieter electric and hybrid cars has created new opportunities — and challenges — for automakers. Even combustion engine vehicles will benefit from newer technologies such as active noise cancellation that could provide complete control over the sounds that people hear inside cars. Drivers and passengers could soon indulge in an audiophile’s dream of playing their favorite music playlist or podcast in monastic silence on the road.

On the other hand, a completely quiet car experience isolated from any sound may actually pose safety risks. After all, most drivers have become accustomed to gauging their driving speed based in part on the changing sounds of their engines. A French study presented at the Proceedings of the Acoustics 2012 Nantes Conference found that drivers tended to underestimate their speed more when they had no sound feedback. That meant the drivers tended to drive faster in situations without having sound to help gauge their actual speed.

Automakers have already begun experimenting with adding artificial engine sounds to electric cars. Some have taken a cue from Hollywood by using futuristic vehicle and spacecraft sounds from science fiction films such as “Star Wars.” Ford has tried out certain “alien spaceship sounds” with some success, says Alex Petniunas, a technical expert in operational sound quality at the Ford Motor Company. Having an audible car sound matters just as much, if not more, for the safety of pedestrians and cyclists as it does for the drivers.

What Car Customers Want

The taming of undesirable car sounds only represents half the battle for drivers’ hearts and minds. In the 1980s, car manufacturers began to seriously study what car customers want in terms of sound. The scientific approach to understanding the psychology of car sounds owes much to the research of acoustic experts working at RWTH Aachen University in Germany during the 1980s. Such experts refined the basic measures for a “psychoacoustic” understanding of how humans psychologically perceive car sounds.

Human brains interpret sounds through four major sound patterns, says Blutner at Synotec Psychoinformatik. First, we gauge the power potential of a sound through its loudness and volume. Second, we understand dynamic potential as a sound’s sharpness, roughness and impulsiveness. A third sound pattern known as emotive potential covers tonality and fluctuation amplitude: the latter being how much a sound varies from its average baseline. The fourth sound pattern, named cognitive potential, describes tonal and temporal shapes, formats, bursts, and sweeps of sound.

“Such key sound patterns can be quite easily measured,” Blutner says. “Therefore a whole string of psychoacoustic measures and signal features are known to describe them.”

A combination of such sound patterns creates the overall sound of each car. Blutner points to how the Porsche engine sound has a “clear, fine sound texture” because of a component called the timing chain that helps control the opening and closing of the engine valves. Without that particular sound pattern, the overall car engine sounds “pale and colorless.”

Automakers think about sound design as a balance between perceptions and expectations of car sounds. Still, acoustic engineers still rely more on experience and instinct than an exact science to find the right sounds for each vehicle model and customer group, Blutner says.

Orchestra rehearsal: Dr. Bernhard Pfäfflin (left) and Bernd Müller are about to perform a sound check on the six-cylinder engine. Credit: Porsche AG

The human brain’s ability to identity specific sound patterns is fairly universal. But any hardwired brain response to such sound patterns in car noises gets heavily filtered through learned cultural perceptions and expectations of cars. People may agree on what sounds loud or sharp in car noises, but their interpretation of those sounds as powerful or pleasant depends on their learned experiences of cars and their cultural backgrounds, says Andre Fiebig, an acoustics researcher at HEAD Acoustics in Germany.

“Sound perception implies the cognitive processing and interpretation of sound and thus cannot be separated from assessment and evaluation of sound,” Fiebig explains.

Marketing research has identified at least 15 subgroups of people who have different preferences for car sounds, says Ercan Altinsoy, chair of Acoustics and Haptics at Dresden University of Technology in Germany. In a 2011 study, he worked with a sports car manufacturer to examine how people judged car sounds according to the idea of “sportiness.” Everyone generally agreed on what audio samples fit the “sporty” car sound patterns. But they split on whether or not they described the sporty sound as pleasant or annoying.

Different cultures also have different car sound preferences. Some high-frequency tones that drive Europeans up the wall sound fairly pleasant to Japanese listeners. Many people in Japan also perceive the sounds of electric cars and hybrid-electric cars as being sporty, whereas Europeans usually associate sportiness with the sound of high-performance combustion engines. Major automakers often tweak the sounds of car models to fit each region’s preferences.

Modern science’s understanding of car sounds remains limited in many ways to a surface-level understanding of psychology. Neuroscientists have made great strides in understanding how the human brain comprehends language and music. By comparison, few academic researchers can get the funding to study car sounds from a similar perspective. If automakers have done such studies, most have not been sharing the results publicly. Still, Altinsoy believes that ongoing acoustic and psychological research on the “language of car sounds” can lead to improved car sound designs in the future.

“We think that car sounds have different components, like in human vocals,” Altinsoy says. “If you bring them together, you can find meaning in them.”

The Startup

Medium's largest active publication, followed by +492K people. Follow to join our community.

Jeremy Hsu

Written by

Science and technology journalist. Military history enthusiast. Asian Groot in Brooklyn. I grew up with video games.

The Startup

Medium's largest active publication, followed by +492K people. Follow to join our community.

Welcome to a place where words matter. On Medium, smart voices and original ideas take center stage - with no ads in sight. Watch
Follow all the topics you care about, and we’ll deliver the best stories for you to your homepage and inbox. Explore
Get unlimited access to the best stories on Medium — and support writers while you’re at it. Just $5/month. Upgrade