Auralization Methodology for External and Internal Truck Sounds

Abstract

Acoustical simulations are useful for work in community noise as well as sound quality. Applications within the respective fields are the auralization of urban vehicle pass bys and the synthesis of engine noise. Endeavours to further develop more efficient transports have created an interest in external sound propagation within urban environments. A model has been constructed for this purpose, auralizing semi-anechoic recordings into a moving source on a generic city street. The amplification from the surroundings have been included as gain factors produced from a ray traced impulse response. Propagation phenomena such as air attenuation, Doppler effect, façade reduction and an indoor room impulse response have been integrated. Output are indoor and outdoor sound files as well as sound pressure level graphs over time and frequency spectra at the peak pressure time instance. To improve the immersion in a driving simulator, the possibility of a sound quality improvement through the use of granular synthesis has been evaluated. In-cab recordings have been manually divided into sections of either acceleration or constant speed based on CAN bus data. An algorithm extracted grains from the sections with pitch periods dependant on engine rpm. Synthesis was performed by overlap-adding based on following a desired rpm profile. Evaluation of the sound files resulting from both applications has been done with a listening test. The urban pass by results were also compared to measurements done in previous work at Landsvägsgatan in Göteborg. In the listening test, sounds were rated mainly by realism. A semantic differential test of realism, annoyance and loudness was used for the urban pass bys as well as a custom pairwise comparison. For the synthesised in-cab engine sounds, a direct pairwise comparison with the existing simulator sounds was done.