Auditory Size Perception in Acoustic Vehicle Alerting Systems (AVAS); Virtual Pitch and Spatial Decorrelation for Heavy Vehicles under Electroacoustic and Environmental Constraints

Abstract

The implementation of Acoustic Vehicle Alerting Systems (AVAS) has expanded as Electric Vehicles (EVs) become increasingly common on the roads. Due to their inherent lower acoustic radiation at low speeds, legislators have put regulatory demands, such as UN Regulation No. 138, on the acoustic radiation of these vehicles. These demands do not, however, differentiate between the type of vehicle, with the same requirements on passenger cars as for heavy electric trucks. This risks removing the auditory cues from the urban environment for differentiating size differences between vehicles, which may have a negative effect on the situational awareness of vulnerable road users and pedestrians, especially apparent for those visually impaired. This thesis investigates auditory cues governing size perception to enhance the perceived size of heavy electric vehicles without increasing urban low-frequency noise pollution or exceeding the physical constraints of standard AVAS speakers. The results of two listening tests are presented: the first was conducted by 17 participants and showed that while spectral balance is the main cue for auditory size perception, spatial decorrelation and time structure also can influence the perceived auditory size of a signal. Further, participants showed a preference for signals containing tonal components over those composed of pure broadband noise. The second test, conducted by 32 participants, applied the findings of the first, focusing on whether virtual pitch and spatial decorrelation could be used to increase the auditory size perception in an applied situation, convolving measured Impulse Responses (IRs) of a currently used AVAS speaker mounted at different positions on a representative truck. The results show that virtual pitch was highly effective at increasing the size perception of the signal, whilst spatial decorrelation was found not to be as effective due to the physical limitations of the implementation. Ultimately, utilizing the missing fundamental phenomenon to simulate virtual pitch allows for enhanced auditory size perception without the addition of low frequency components, effectively conveying vehicle mass without worsening urban noise pollution