This is the sound of an electric car

source: Audi AG

As of summer 2019, all newly registered electric and hybrid cars in the EU need to make artificial noise. It’s high time to ask the Audi sound designers how they mix the sound. We’ll give you a hint: a didgeridoo could be heard echoing through the office.

Three laptops. Three computer screens. Three speakers. Mixers, amplifiers, and cables in every color. That’s what the desk of Audi sound designer Rudi Halbmeir looks like. Behind him, a didgeridoo, a guitar, a violin bow, and a keyboard lean against a shelf. Are we in a sound studio? It sometimes seems that way to his employees in the open-plan office. And in a way, it’s true. That’s because, at his desk, Halbmeir is mixing the sounds used for external noise — for cars like the  Audi e-tron for China and the USA.

The highlight of his office? Under his desk, you’ll find a gas pedal and a speaker that allow him to accelerate a fictional e-tron and hear the sound at the same time. He presses the pedal down, the sound gets louder, virtual amplitudes spike on the monitor… goosebumps. For Halbmeir, it’s all in a day’s work. He turns a few mixer knobs and clicks through the soundtracks. “We wrote the user interface ourselves. Back then, what we wanted wasn’t being sold yet.” So he has a home-made sound studio at his desk. After all, buying off the rack is something anyone can do.

The Audi e-tron’s external sound, for example, is created from over 30 different sound recordings that are layered on top of each other.” – Rudi Halbmeir, sound designer

How electric car sounds are designed

Since 2009, Halbmeir has been responsible for the acoustics in the Audi models. After training as an electrician and getting a degree in mechanical engineering, he turned his hobby into a job. “I play seven instruments and have a sound studio at home. My boss back then thought: that might just be a good fit,” he says with a grin.

Since then, he’s built a database of more than 100 sound files and tones.  “There are different synth sounds as well as recorded highway traffic noises in there. I like to experiment. What makes a good sound? Playing the guitar with the violin bow, or didgeridoo sounds,” Halbmeir reveals, and plays a long tone on the didgeridoo to prove his point.

The sound reacts to the motion of the electric car

How does the perfect external noise for the Audi e-tron sound? In whatever environment the electric car is in, it must and should draw attention. According to EU regulations, the sounds need to be clearly audible up to a speed of 20 km/h. In the USA, they are required until 31 km/h. They signal to pedestrians and bicyclists that a car is approaching, accelerating, or braking. “We do that not only with volume but also with a changing sound,” explains Halbmeir. The brain quickly labels monotonous, unchanging sounds as “normal” background noise.

Sound design up close — how does an electric car sound?

The sound shouldn’t come across as annoying or unpleasant. Frequency and volume are critical. The deciding factor is finding the right mix of tones that create the sound. “It’s almost like a symphony. The Audi e-tron’s external sound, for example, is created from over 30 different sound recordings that are layered on top of each other. 15 of them are always played at any given time. I call the type of sound “realistic-technical,” not too harmonic. Otherwise people won’t be consciously aware of the sound,” explains Halbmeir.

He uses his intuition while composing: “I let the different tones lead the way. I sense, hear, and feel the music. My gut is often more important than my ear.”

Keep your ears perked — testing the e-tron sound

In the sound lab, Stephan Gsell and Rudi Halbmeir test the sound not only at the desk but in a model: one equipped with Audi e-tron technology. “That is very important, because the speakers are different and the noises sound very different coming out of the car,” explains Halbmeir. To use it, the two go into the Audi sound lab. “The sound lab is a semi-anechoic chamber. That means that the room reflects almost no sound from the ceiling and the walls, but has a normal, sound-reflecting asphalt floor,” explains Gsell. He holds a doctorate in electrical engineering and has been part of the acoustics team since 2015.

The lab looks futuristic with the foam wedges on the walls and ceilings. In the middle of it all, an e-tron technology demo model is surrounded by small microphones. Our voices nearly disappear into the room. It feels a bit like being in an airplane or wearing noise-canceling headphones.

The right sound for every move in the electric car

“If you drive Audi, you should hear Audi.” – Stephan Gsell, sound designer

Where is the external sound hidden on the e-tron? A small speaker is located in front of the right front wheel. If the car drives backward, or faster, the level increases and the noise gets louder. The sound is dynamically adjusted according to the driving parameters, such as speed or weight. “The noise should not just meet the legal requirements; it should also be pleasant to listen to and just be a nice sound overall. If you drive Audi, you should hear Audi,” says Gsell, the sound designer.

The vehicle acoustics department made a conscious decision to avoid the acoustic characteristics of a conventional non-electric car when it came to the e-tron. “The e-tron should sound like an electric car, not imitate a combustion engine,” says Halbmeir. Here’s an interesting fact: because of the varying level requirements, the first Audi electric car will sound exactly the same in the EU and in China, but the US version will sound different.

Paradoxes in sound design: once quiet, now loud

Halbmeir listens to the e-tron sound one more time and says with a wink: “It’s funny, it used to be my job to make the cars as quiet as possible. Now I have to make it louder with artificial sounds.”