Quality Comparison of Dynamic Auditory Virtual-Reality Simulation Approaches of Approaching Vehicles Regarding Perceptual Behavior and Psychoacoustic Values

Bazilinskyy P., Merino-Martínez R., Özcan E., Dodou D., de Winter J.

Exterior vehicle sounds have been introduced in electric vehicles and as external human–machine interfaces for automated vehicles. While previous research has studied the effect of exterior vehicle sounds on detectability and acceptance, the present study takes on a different approach by examining the efficacy of such sounds in deterring people from crossing the road. An online study was conducted in which 226 participants were presented with different types of synthetic sounds, including sounds of a combustion engine, pure tones, combined tones, and beeps. Participants were presented with a scenario where a vehicle moved in a straight trajectory at a constant velocity of 30 km/h, without any accompanying visual information. Participants, acting as pedestrians, were asked to hold down a key when they felt safe to cross. After each trial, they assessed whether the vehicle sound was easy to notice, whether it gave enough information to realize that a vehicle was approaching, and whether the sound was annoying. The results showed that sounds of higher modeled perceived loudness, such as continuous tones with high frequency, were the most effective in deterring participants from crossing the road. The tested intermittent beeps resulted in lower crossing deterrence than continuous tones, presumably because no valuable information could be derived during the inter-pulse intervals. Tire noise proved to be effective in deterring participants from crossing while being the least annoying among the sounds tested. These results may prove insightful for the improvement of synthetic exterior vehicle sounds.

Wessels M., Kröling S., Oberfeld D.

• The sound of an accelerating ICEV helps pedestrians judge its TTC fairly accurately. • Comparatively, more erroneous (overestimated) TTC estimates for accelerating EVs. • An acoustic vehicle altering system (AVAS) only partly compensates for these errors. • In real traffic, TTC overestimations might lead to risky road-crossing decisions. To avoid collisions, pedestrians intending to cross a road need to accurately estimate the time-to-collision (TTC) of an approaching vehicle. For TTC estimation, auditory information can be considered particularly relevant when the approaching vehicle accelerates. The sound of vehicles with internal combustion engine (ICEVs) provides characteristic auditory information about the acceleration state (increasing rotational speed and engine load). However, for electric vehicles (EVs), the acoustic signature during acceleration is less salient. Although the auditory detection of EVs has been studied extensively, there is no research on potential effects of the altered acoustic signature of EVs on TTC estimation. To close this gap, we compared TTC estimates for ICEVs and for EVs with and without activated acoustic vehicle alerting system (AVAS). We implemented a novel interactive audiovisual virtual-reality system for studying the human perception of approaching vehicles. Using acoustic recordings of real vehicles as source signals, the dynamic spatial sound field corresponding to a vehicle approaching in an urban setting is generated based on physical modeling of the sound propagation between vehicle and pedestrian (listener) and is presented via sound field synthesis (higher-order Ambisonics). In addition to the auditory simulations, the scene was visually presented on a head-mounted display with head tracking. Participants estimated the TTC of vehicles that either approached at a constant speed or accelerated positively. In conditions with constant speed, TTC estimates for EVs with and without AVAS were similar to those for ICEVs. In contrast, for accelerating vehicles, there was a substantial effect of the vehicle type on the TTC estimates. For the EVs, the mean TTC estimates showed a significant overestimation. Thus, subjects on average perceived the time of arrival of the EV at their position as longer than it actually was. The extent of overestimation increased with acceleration and presented TTC. This pattern is similar to a first-order TTC estimation representing a failure to consider the acceleration, which is consistently reported in the literature for visual-only presentations of accelerating objects. In comparison, the overestimation of TTC was largely reduced for the accelerating ICEVs. The AVAS somewhat improved the TTC estimates for the accelerating EVs, but without reaching the same level of accuracy as for the ICEVs. In real traffic scenarios, overestimations of the TTC of approaching vehicles might lead to risky road-crossing decisions. Therefore, our finding that pedestrians are significantly less able to use the acoustic information emitted by accelerating EVs for their TTC judgments, compared to accelerating ICEVs, has important implications for road safety and for the design of AVAS technologies.

Oberfeld D., Wessels M., Büttner D.

To avoid collision, pedestrians intending to cross a road need to estimate the time-to-collision (TTC) of an approaching vehicle. Here, we present a novel interactive audiovisual virtual-reality system for investigating how the acoustic characteristics (loudness and engine type) of vehicles influence the TTC estimation. Using acoustic recordings of real vehicles as source signals, the dynamic spatial sound fields corresponding to a vehicle approaching in an urban setting are generated based on physical modeling of the sound propagation between vehicle and pedestrian and are presented via sound field synthesis. We studied TTC estimation for vehicles with internal combustion engine and for loudness-matched electric vehicles. The vehicle sound levels were varied by 10 dB, independently of the speed, presented TTC, and vehicle type. In an auditory-only condition, the cars were not visible, and lower loudness of the cars resulted in considerably longer TTC estimates. Importantly, the loudness of the cars also had a significant effect in the same direction on the TTC estimates in an audiovisual condition, where the cars were additionally visually presented via interactive virtual-reality simulations. Thus, pedestrians use auditory information when estimating TTC, even when full visual information is available. At equal loudness, the TTC judgments for electric and conventional vehicles were virtually identical, indicating that loudness has a stronger effect than spectral differences. Because TTC overestimations can result in risky road crossing decisions, the results imply that vehicle loudness should be considered as an important factor in pedestrian safety.

Wessels M., Zähme C., Oberfeld D.

To cross a road safely, pedestrians estimate the time remaining until an approaching vehicle arrives at their location (time-to-collision, TTC). For visually presented accelerated objects, however, TTC estimates are known to show a first-order pattern indicating that acceleration is not adequately considered. We investigated whether added vehicle sound can reduce these estimation errors. Twenty-five participants estimated the TTC of vehicles approaching with constant velocity or accelerating, from a pedestrian’s perspective at the curb in a traffic simulation. For visually-only presented accelerating vehicles, the TTC estimates showed the expected first-order pattern and thus large estimation errors. With added vehicle sound, the first-order pattern was largely removed, and TTC estimates were significantly more accurate compared to the visual-only presentation. For constant velocities, TTC estimates in both presentation conditions were predominantly accurate. Taken together, the sound of an accelerating vehicle can compensate for erroneous visual TTC estimates presumably by promoting the consideration of acceleration.

Steinbach L., Altinsoy M.E.

Road traffic noise is the most annoying form of environmental noise pollution. The enforcement of using artificially generated sound for electrically powered vehicles is currently on the rise. In this regard, it is important to know if an additional stationary sound could be conducive to earlier detection. The aim of this project was to gather information on the influence of artificially generated stationary sound with an Acoustic Vehicle Alerting System (AVAS) of electrically driven vehicles on the safety of other traffic participants. The stationary sound of an electric vehicle denotes a sound corresponding to the idling noise of a conventional combustion vehicle. It indicates that a vehicle is stationary (v = 0 km/h) but the engine is running. Furthermore, the aim was to be investigated whether a stationary sound can contribute to the prevention of accidents. Various safety-relevant traffic situations, different stationary sounds and also driving sounds were used for this purpose. However, the question of whether a stationary sound would improve road safety for visually impaired pedestrians has not yet been addressed. The results of the study show that not every stationary sound in any driving situation leads to a better detection. Some stationary sounds show significant effects regarding the detection performance. Both laboratory tests and field tests have shown that there are stationary sound combinations which enable an earlier detection. Furthermore, an inappropriate stationary sound can also lead to a later detection. It has been found that clear differences e.g. due to level differences or frequency shifts between driving and stationary sound could lead to earlier detection.

Kaplanis N., Bech S., Lokki T., van Waterschoot T., Holdt Jensen S.

An experiment was conducted to identify the perceptual effects of acoustical properties of domestic listening environments, in a stereophonic reproduction scenario. Nine sound fields, originating from four rooms, were captured and spatially reproduced over a three-dimensional loudspeaker array. A panel of ten expert assessors identified and quantified the perceived differences of those sound fields using their own perceptual attributes. A multivariate analysis revealed two principal dimensions that could summarize the sound fields of this investigation. Four perceptual constructs seem to characterize the sensory properties of these dimensions, relating to Reverberance, Width & Envelopment, Proximity, and Bass. Overall, the results signify the importance of reverberation in residential listening environments on the perceived sensory experience, and as a consequence, the assessors' preferences towards certain decay times.

Grimm G., Luberadzka J., Hohmann V.

Singh S., Payne S.R., Mackrill J.B., Jennings P.A.

New laws stipulate that electric vehicles must emit additional sounds to alert pedestrians of the vehicles’ approach to prevent potential collisions. These new sounds will also influence pedestrians’ impression of the vehicle brand. A methodology has been developed to evaluate electric vehicle (EV) sounds in a virtual-world environment by assessing; (a) detectability and recognisability to ensure pedestrians’ safety, and (b) emotional evaluation of the sound quality to determine its impact on the perception of the vehicle brand. This experimental study examines external validity of the methodology. Fourteen participants evaluated an EV, emitting three sounds, in a traffic scenario in a real-world and a virtual-world environment. The traffic scenario involved a pedestrian ‘standing’ at a residential road junction while the EV travelled at 12 mph from behind the pedestrian, arriving at the junction at one of two pre-set times. Results show that the presented virtual-world methodology accurately predicts pedestrians’ evaluation of detectability of EV sounds and powerfulness and pleasantness of the vehicle brand in the corresponding real-world scenario. It also predicts the ranked order of sounds in the real-world for detection distance and recognisability. Arguably, for similar methods and setups, virtual-worlds would effectively predict pedestrians’ evaluation in the real-world. Interestingly, varying a vehicle’s arrival time, just like a real-world scenario, is found to affect pedestrians’ detection rate. Unlike experiments in the real-world, the presented methodology for experiments in virtual-world benefits from being reliable, quick, easy to implement, with more experimental control and options to easily manipulate any experiment variables.

Spors S., Wierstorf H., Raake A., Melchior F., Frank M., Zotter F.

This paper reviews the current state of loudspeaker-based spatial sound reproduction methods from technical perspective as well as perceptual perspective. A nomenclature is developed that allows for a strict separation between these two perspectives. The physical fundamentals, practical realization, and results from perceptual studies are discussed for a number of well-established and emerging reproduction techniques. Further, the paper outlines novel approaches to spatial sound evaluation in terms of perceived quality and provides a comparison of current approaches.

Wall Emerson R., Kim D.S., Naghshineh K., Pliskow J., Myers K.

AbstractThis paper examines participants who are blind, with and without normal hearing, regarding detection of forward approaching and backing vehicles operating in electric mode (identified in this paper as quiet vehicles) under low speed conditions. Testing under low ambient sound conditions involved evaluation of internal combustion engine vehicles, hybrid vehicles operating in electric mode (EM), and the same hybrid vehicles operating in EM but with five different artificially generated sounds. Three of the five artificial sounds improved detection relative to the internal combustion engine condition for both forward and backward detection tasks. Regression analysis indicated that significant predictors of forward detection performance include average wind speed, amplitude modulation of the signal, hearing loss in the 500 Hz range, vehicle velocity, minimum ambient sound level, and overall vehicle sound level in units of A-weighted decibels. The corresponding analysis for backward detection indicated...

Pörschmann C., Störig C.

Cohen J.

One possible reason for the continued neglect of statistical power analysis in research in the behavioral sciences is the inaccessibility of or difficulty with the standard material. A convenient, although not comprehensive, presentation of required sample sizes is provided here. Effect-size indexes and conventional values for these are given for operationally defined small, medium, and large effects. The sample sizes necessary for .80 power to detect effects at these levels are tabled for eight standard statistical tests: (a) the difference between independent means, (b) the significance of a product-moment correlation, (c) the difference between independent rs, (d) the sign test, (e) the difference between independent proportions, (f) chi-square tests for goodness of fit and contingency tables, (g) one-way analysis of variance, and (h) the significance of a multiple or multiple partial correlation.

Guastavino C., Katz B.F.

Perceptual differences between sound reproduction systems with multiple spatial dimensions have been investigated. Two blind studies were performed using system configurations involving 1-D, 2-D, and 3-D loudspeaker arrays. Various types of source material were used, ranging from urban soundscapes to musical passages. Experiment I consisted in collecting subjects’ perceptions in a free-response format to identify relevant criteria for multi-dimensional spatial sound reproduction of complex auditory scenes by means of linguistic analysis. Experiment II utilized both free response and scale judgments for seven parameters derived form Experiment I. Results indicated a strong correlation between the source material (sound scene) and the subjective evaluation of the parameters, making the notion of an “optimal” reproduction method difficult for arbitrary source material.

Jenison R.L.

Specific details of acoustic information that support the perception of moving sound sources are presented. The analyses demonstrate that higher order variables related to moving sound sources such as position, velocity, and time-to-arrival are observable from conjoint measurement of the time-varying acoustic variables of interaural-time delay, Doppler shift, and average sound intensity. Motion structures the ambient acoustic array in such a way that the measured variables under consideration sufficiently specify motion kinematics when the system of forward equations, combined with their first-order differentials with respect to time, are inverted.

Allen J.B., Berkley D.A.

Image methods are commonly used for the analysis of the acoustic properties of enclosures. In this paper we discuss the theoretical and practical use of image techniques for simulating, on a digital computer, the impulse response between two points in a small rectangular room. The resulting impulse response, when convolved with any desired input signal, such as speech, simulates room reverberation of the input signal. This technique is useful in signal processing or psychoacoustic studies. The entire process is carried out on a digital computer so that a wide range of room parameters can be studied with accurate control over the experimental conditions. A fortran implementation of this model has been included.