AVAS:
Sound Design for Electric Vehicles under UN ECE R138
Electric vehicles are too quiet, that was the problem. The solution is a mandated sound. What the regulation frames as a safety requirement is simultaneously the biggest unused brand opportunity in automotive: the first sound a person hears from your car, before they see it.
The short version
AVAS has been mandatory for years, not upcoming. The regulation prescribes physical limits, not musical ones. Within 56 to 75 dB(A), 0 to 20 km/h, and a defined frequency rise, the design latitude is large, and most manufacturers do not use it.
Contents
1. What the regulation actually requires
AVAS stands for Acoustic Vehicle Alerting System. In the EU, UN ECE R138 sets the requirements. It has been mandatory since 1 July 2019 for newly type-approved vehicles and since 1 July 2021 for all new registrations of electric and hybrid vehicles.
| Requirement | Specification | Purpose |
|---|---|---|
| Speed range | 0 to roughly 20 km/h | Above that, tyre and wind noise take over |
| Minimum level | 56 dB(A) | Audibility in urban noise |
| Maximum level | 75 dB(A) | Protection against noise pollution |
| Frequency shift | more than 0.8 % per km/h | Acceleration has to be audible |
| Direction | forwards and in reverse | Reversing is the most critical case |
The frequency shift is the most interesting requirement, because it governs a perceptual question rather than a level. A pedestrian must be able to hear whether the vehicle is accelerating or slowing. A constant tone cannot do that, which is why coupling pitch to speed is written into the rule explicitly.
2. Why compliance is the easy part
Meeting the limits is a measurement problem and therefore solvable. Modules on the market do exactly that, and anyone who only needs homologation buys one and is finished.
You know the result. A synthetic tone somewhere between spaceship and kitchen appliance, chosen by nobody, making a statement about your brand every time the car pulls away that you never wrote. On a vehicle whose interior was optimised for months on material perception, that is a remarkable discontinuity.
The point we keep making to OEMs: AVAS is the only sound of your vehicle that people hear from outside before they buy it. Engine sound was a central brand signal for decades. On electric vehicles, AVAS inherits that role, and in many projects it is treated as a component rather than as a brand element.
3. The brand sound inside the mandatory noise
Within the limits, plenty of decisions remain open, and every one of them is a brand statement.
- Timbre. Harmonic or noise-based, warm or metallic. A luxury marque needs a different answer here than a commercial vehicle.
- Character of the frequency curve. The coupling to speed has to exist, its shape does not have to be linear. A slightly progressive curve reads as composed, a steep one reads as anxious.
- Behaviour at standstill. The moment when the vehicle is ready but not moving is the most interesting design opportunity, and it is frequently left empty.
- Reverse. Has to be distinguishable without sounding like construction machinery. This is where craft separates from module.
- Relationship to interior sound. If outside and inside come from two different worlds, the driver notices without being able to name it.
The discipline lies in not becoming conspicuous. An AVAS sound perceived as design has failed. It should sound functionally self-evident and still be attributable. That is the same task as a good sound logo, with a safety requirement on top.
AVAS development with brand ambition
We develop AVAS sounds within the limits of UN ECE R138 and FMVSS 141, aligned with your acoustic brand identity. Experience from automotive projects including Porsche.
Request an AVAS project →4. How an AVAS sound is developed
- Brand briefing and sonic direction. Which attributes should the vehicle assert acoustically? Three to five directions as audible sketches, not as a list of adjectives.
- Parametric design. The sound is not built as an audio file but as a system of parameters responding to speed. That is the essential difference from conventional sound design.
- Implementation in the control unit. Limited processing, limited memory, defined interfaces. This is where creative concepts that worked in the studio fail.
- Vehicle validation. How does it sound in reality, with this speaker, at this position, on this vehicle? Regularly different from expectations.
- Measurement campaign and homologation. Demonstrating the limits under defined conditions.
- Fine tuning. The part that decides between good and very good, and the part there is often no time left for.
The most important sentence about this process: step two determines everything that follows. A sound conceived as a parametric system can be tuned. A sound delivered as a finished file can only be replaced.
5. R138 versus FMVSS 141
Anyone shipping internationally needs both. The requirements are related but not identical, and the difference lives in the details of measurement procedures and band requirements.
In practice this means a sonic concept developed against only one of the two regulations can fail the other, or has to be adapted so far that the brand effect suffers. The efficient route is to carry both rulebooks as boundary conditions in the parametric design from the start, rather than improvising an export variant later.
That is unglamorous, but it saves an entire iteration cycle, and iteration cycles are the real currency in OEM projects.
6. Timeline in an OEM project
Realistic orientation from sonic direction to homologation-ready state:
| Phase | Duration |
|---|---|
| Sonic direction and selection | 4 to 8 weeks |
| Parametric design | 4 to 10 weeks |
| Implementation and integration | 6 to 16 weeks |
| Validation and measurement | 4 to 12 weeks |
The most common planning error is starting AVAS too late. If the topic only surfaces when homologation is due, the standard module is the only option left, because there is no time for design. The sound then gets decided by a schedule rather than by your brand.
Anchor AVAS early in the vehicle programme and you end up with the same cost and a result that matches the rest of the car. That is the whole message of this article.
Research, source selection, and editorial responsibility: Rahim Erbil. We used AI while drafting and researching. Every sentence was checked by hand before it landed here. Made with Herzblut and AI.
Related reading:
The same name on every line.
Concept, composition, sound design, mix, master: at Campera Media your project passes through one pair of hands, from the first briefing to the last second of the fade-out.
Meet Rahim →Common questions about
AVAS.
In the EU, the requirement under UN ECE R138 has applied since 1 July 2019 for newly type-approved vehicles and since 1 July 2021 for all new registrations of electric and hybrid vehicles. So it is not an upcoming topic but series reality and has been for years.
Sound level must be at least 56 dB(A) and must not exceed 75 dB(A). The sound must be generated in the speed range from 0 to roughly 20 km/h, forwards and in reverse. In addition, frequency has to rise with speed, by more than 0.8 percent per km/h, so that acceleration becomes audible.
Yes, and that is where the real opportunity lies. The regulation defines physical boundary conditions, not musical ones. Within those limits there is enormous design latitude, and many manufacturers still give it away by fitting a standard module.
Expect three to nine months from sonic direction to a homologation-ready state, depending on review cycles and measurement campaigns. The creative part is the shorter one, in-vehicle validation and measurement consume the time.
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