Implementing digital engine sound enhancement techniques to ...

Figure 2 - Design & Test Process with LEA & ASD (Active Sound Design) ModulesFigure 3 - Example of how target orders are enhanced within ASD Module3. Chrysler experience of engine sound design3.1 Background/ChallengeThe Interior sound signature of the new proposed sporty variant of a production vehicle did notmeet the target image sound expected in the sport segment. Chrysler desired a more competitive andsporty sound to differentiate this product in the marketplace. Since the vehicle architecture wasalready in existence, sound enhancement solutions were limited to re-tuning induction and exhaust.Exhaust tuning options were very limited since the vehicle was already close to the legal pass-byrequirements. Designing/fabricating and testing a new exhaust tuning code was beyond the allocatedbudget, and outside the scope for timing. Opportunities explored for induction tuning did not resultin a major sound quality improvement.4

Figure 4 - Comparison of Base Vs. Base Vehicle w/V8 sound enhancementOnce the desired sound profile is finalized, the resulting BOX file is ready for productionimplementation. This is done by embedding the corresponding run-time script file within the DSP ofthe Audio Processor.3.5 Results of Chrysler experienceEngineering sound enhancement technology via the existing audio system is a very powerful,effective and low-risk solution to achieve the desired character in a vehicle. Besides being a verylow-cost solution, it is much quicker to implement than redesigning/retuning/modifying induction,exhaust and other hardware, which carries the risk of degrading functionality, pass-by requirements,etc.In addition to just basic sound enrichment, it can easily be used in a number of otherareas/applications including:- Enabling additional modes on vehicle (Super-Sport/ Sport / Eco, etc.)- Cylinder De-activation (add back normal firing orders)- Cold Engine Mode (mask un-desired content)- Electric Vehicle (add normal/sporty driving modes to replicate a firing engine)- HEV switching to electric mode (mask transient)- Towing (mask un-desired content)- Exterior Noise (add exterior weather-resistant speakers to enhance exhaust note)- Diagnostic message relay (Convey diagnostic messages from the CAN Bus)4. Renault R-Sound effect experience with CLIO4.1 Feature descriptionRenault’s R-Sound Effect feature is embedded in the new 2013 CLIO 4 multimedia system. Itoffers the Driver a choice from various pre-programmed engine sounds via the Man Machinegraphical Interface (MMI) illustrated in Figure 5. Shown are 3 example profiles (of 6 available) thatillustrate different sound designs based on existing, theoretical and futuristic products.6

Figure 5 - Man Machine graphical Interface (MMI) of R-sound Effect4.2 Sound design processThe Renault team clearly identifies 3 types of sound design processes for automotive sounds.- First one based on existing vehicles and engines- Second one based on expert’s knowledge and numerical simulations- Third one based on product intentionsThe main process is based on recording, analyzing, and then synthesizing an existing car and thenusing it to propose designed sounds. In this process, we focus on recognition of sound and accept afew modifications in order to keep it compatible with a majority of audio systems. The frequencycomponents in the final sound are similar to the recorded sound.This process leads to “rich components” as shown in figure 6. Rich component means that thespectrum is composed of many orders and each order level varies very quickly with engine speed.Figure 6 - typical order analysis of sound obtained by measurementThe second sound design approach is based on theoretical harmonic creation. Engine expertsknow which engine order is generated by a specific architecture (V6, V8, L4 …). We use numericalsimulation to calculate each engine order level for each RPM, from mobile masses efforts andcombustion force. This approach leads to “pure component” spectrums as figure 7, each order levelis varying slowly as RPM changes and it presents less that 10 or 15 orders (more is possible forspecific engines). In our case we use this kind of sound design process to propose a motorcyclesound; as Renault is not a motorcycle manufacturer so we decided to propose a theoretical sound.Figure 7 - typical order analysis of sound obtained by an expert approachThe third sound design strategy is based on product intention and leads to a pure sound creation.We used this method to propose a specific sound for the space shuttle or a UFO that is clearlyimpossible to measure. We don’t have any in-house expert to design this sound, and the unique7

guideline is to design the sound of a UFO as the customer would expect to drive it. This process issimilar to VSP sound designed for Electrical Vehicle where constraints lead to imagined sounds fromwords or intentions [10] [11]. The creation of this kind of sound faces multiple difficulties; one ofthe most important is that the sound interpretation for each person leads to different aesthetic choicesand cultural aspects being also not insignificant.All these 3 processes are very different, and graphically represented in figure 8.Need analysis toolsNeed simulation toolsClio V6, analyzesound design processObject axeExistingMotocycle, ExpertIn mindsound design processAnalyseCreationSound axeVery Old Car ?Out of mindUnrealisticUFO, Product sounddesign processNeed creation toolsFigure 8 – Sound/Object 2D graph4.3 Sound choiceDuring R-sound development a lot of proposed sounds are generated with suggestions from manyemployees. This activity is treated internally more like a “sound design championship”. Since all theproposed sounds cannot be implemented, a few select sounds are shortlisted via a jury panel to beimplemented in the MMI.The choice is probably the most difficult stage of the process and in addition to acoustic andtechnical constraints, trademark laws have to be considered. We can only use images of Renaultgroup vehicles and unbranded vehicles (as UFO or unbranded motorcycle). Then for recent vehiclesthe link between image and sound is driven by the existing sound (as Clio V6) and the choice isreduced to the binary possibility: do we propose this vehicle to our customer, yes or no?The choice is more difficult for simulated sounds. A jury was used to achieve the final list ofsounds and images, and consisted of style (graphical design), marketing, vehicle project leader,product definition, customer satisfaction and 2 acousticians (the people who proposed the soundswere excluded from this jury).The choice for futuristic sound is even more difficult. The first question is whether to propose aUFO sound or not? Experts who work on engine sound for a long time are clearly against this kind of“non physical sound”, but marketing and designers accept this as an amusing approach totally inphase with the R-Sound effect product. When we decided to propose an UFO in our MMI thequestion was: what should be the sound of an UFO? Then the sound designer team proposed soundsand let the jury picked the final sound.4.4 Sounds ValidationValidating sounds is quite easy with appropriate tools, and it’s clear that it is impossible to8

validate this kind of sound with a standard jury testing in a laboratory. The validation must bedynamic, in car and with different levels. We ask ourselves the following questions:- Sound quality level, is the sound pleasant? Is the sound coherent with image? (recognition)- Is the sound able to provide additional sensations? (clearly different with original vehiclesound and audible)- Is the sound adapted to every usage of the vehicle?- We also consider that this kind of enhancement must respect security aspects, and we checkthat every sound leads to enhance pleasure for the lowest speeds. Thus we reduce the level ofenhancement as the speed vehicle increase.It’s important to notice that the validation and fine tuning of each sound is an iterative processwith in vehicle test driving, measurement and new design until achievement of each validationparameter. The process has been meanly repeated three times for each sound to get the right sound.After that, the porting and implementation was done with a car audio supplier and the Clio 4 with the6 different new sounds is now available on the market since 2013.5. CONCLUSIONWe explored a complete Sound Design of Engine Sound process from sound recording tosound generation by using the audio stereo system. This process, based on digital signal processing,has the following advantages: Cost: The algorithm doesn’t require a lot of computation power. It’s much cheaper than amechanical solution. Freedom: The sound designer has no mechanical constraint; the sound can be completelynew. Flexibility: The algorithm and the data set of sound synthesis can be uploaded at the endof the car’s project life. The sound design can be created in parallel with themechanical design. The same sound design can also be applied to different vehicles. Choice: It’s possible to give the choice to the driver among several data sets for differentsound designs. Adaptation: The sound design can be adapted to different drivers’ preferences. The sounddesign can also have other parameters to reduce the engine sound enhancement, forinstance if the driver decides to listen to music on the car audio system. Environment: The sound design by embedded sound synthesis is a chip only weighing afew ounces, easily recyclable, with less CO2 to manufacture than a mechanical solution.In addition, this solution doesn’t produce any noise annoyance outside of the car. Performance: Because it’s very small and very light, performances like acceleration arebetter. Fuel consumption and CO2 emission are also lower than with a mechanicalsolution.Product development experience at Chrysler Group LLC in USA and implementation experienceat Renault in France validates the ease and flexibility of sound design, audio playback andimplementation in-vehicle. In both cases, feedback from the hands-on development experience hasbeen over-whelming positive in achieving the final goal of enhancing the driver’s audio experience.This technology appears to be ready for prime-time production implementation, with the biggestchallenge being on how to market this feature with potential vehicle buyers in marketplace.6. REFERENCES[1] Emilie Poirson, Jean-François Petiot, Florent Richard « A method for perceptual evaluationof products by naive subjects - application to car engine sounds” published in "International Journalof Industrial Ergonomics 40, 5 (2010) 504-516"[2] Florent Richard, Vincent Roussarie “ Design de l’ambiance sonore d’un véhicule automobile– Méthode et outil pour le contrôle de la coloration moteur” published in "Acoustique et TechniqueSpecial “Design Sonore” n°41 (2005) 16--19"[3] N. Kubo “Types of Car Sound Quality categorized by Frequency Dynamics”, ICSV16,Krakow9

[4] B. Le Nindre “ Typage sonore identitaire : le cas du véhicule sportif “ published in"Acoustique et Technique Special “Design Sonore” n°41 (2005) 20-23"[5] Leo L. Beranek, “Criteria for noise and vibration in communities, buildings, and vehicles,”Chap. 17 in Noise and Vibration Control Engineering Principles and Applications, edited by Leo L.Beranek and Istvan L. Ver (Wiley, New York, 1992).[6] Bernard Widrow and Samuel D. Steams, Adaptive Signal Processing (Prentice-Hall,Englewood Cliffs, New Jersey, 1985).[7] T. F. W. Embleton, “Tutorial on sound propagation outdoors,” J. Acoust. Soc. Am., 100(7),31-48 (1996).[8] M. Stinson and G. Daigle, “Meteorological measurements for use in sound propagationcalculations,” Proc. 7th Long Range Sound Propagation, 137-147 (1996).[9] M. Nishimura, M. Kondo, K. Iwamoto and Y. Tsujimoto, “Active attenuation of impulsivenoise from a railway tunnel exit,” Proc. INTER-NOISE 94, 1383-1388 (1994).[10] Le Nindre B., Guyader G., “EV- sound quality: customer expectations and fears - crucialNVH stakes”, Proceedings of SIA conference (Société des Ingénieurs de l’Automobile), Saint -Ouen,France, 2010.[11] N. Misdariis, A. Cera, E. Levallois, C. Locqueteau, Do electric cars have to make noise? Anemblematic opportunity for designing sounds and soundscapes, Proceedings ACOUSTICS 2012 ,Paris , France , 201210