With the advent of virtual reality (VR) technology, spatial audio has been increasingly adopted to evaluate the acoustic environment in soundscape research. It is therefore imperative to assess the quality of commonly used spatial audio reproduction methods to determine their ecological validity. Through subjective evaluations with 30 participants, the same participant evaluated four outdoor in situ locations vis-à-vis its corresponding audio-visual recording in VR on a separate day. A total of three spatial audio reproduction methods were assessed in VR, and they were all down-mixed from the first-order ambisonics (FOA) recordings to headphonebased FOA-static binaural, FOA-tracked binaural; and FOA 2-dimensional (2D) octagonal speaker array. The participants evaluated the acoustic environment in terms of the overall soundscape quality and perceived spatial qualities at each location. Regarding overall soundscape quality, there were no significant differences in evaluating the sound-source dominance and affective soundscape qualities between in situ and all VR methods. However, significant differences were found in the perceived spatial qualities between three reproduction methods and in situ. Among the source-related spatial attributes, the perceived distance of the dominating sounds was farther in the virtual than in the in situ evaluations. In the localization of sound sources, both the FOA-tracked binaural and the FOA-2D speaker array exhibited higher spatial acoustic fidelity than FOA-static binaural. Regarding the environment-related spatial quality attributes, the 2D speaker array reproduction was perceived as more immersive and realistic than other reproduction methods. Overall, the FOA-tracked binaural appears to exhibit sufficient fidelity for cinematic VR evaluation of soundscapes.
Featured Application: This review introduces the concept of spatial audio in the perspective of soundscape practitioners. A selection guide based on the spatial fidelity and degree of perceptual accuracy of the mentioned spatial audio recording and reproduction techniques is also provided.Abstract: With the advancement of spatial audio technologies, in both recording and reproduction, we are seeing more applications that incorporate 3D sound to create an immersive aural experience. Soundscape design and evaluation for urban planning can now tap into the extensive spatial audio tools for sound capture and 3D sound rendering over headphones and speaker arrays. In this paper, we outline a list of available state-of-the-art spatial audio recording techniques and devices, spatial audio physical and perceptual reproduction techniques, emerging spatial audio techniques for virtual and augmented reality, followed by a discussion on the degree of perceptual accuracy of recording and reproduction techniques in representing the acoustic environment.
Introducing pleasant natural sounds to mask urban noises is an important soundscape design strategy to improve acoustic comfort. This study investigates the effects of signal-to-noise ratio (SNR) between natural sounds (signal) and the target noises (noise) and their temporal characteristics on the perceived loudness of noise (PLN) and overall soundscape quality (OSQ) through a laboratory experiment. Two types of urban noise sources (hydraulic breaker and traffic noises) were set to A-weighted equivalent sound pressure levels (SPL) of 55, 65, and 75 dB and then augmented with two types of natural sounds (birdsong and stream), across a range of SNRs. Each acoustic stimulus was a combination of noise and natural sound at SNRs from −6 to 6 dB. Averaged across all cases, the subjective assessment of PLN showed that augmenting urban noise separately with the two natural sounds reduced the PLN by 17.9%, with no significant differences found between the birdsong and stream sounds. Adding natural sounds increased the OSQ by on average 18.3% across the cases, but their effects gradually decreased as the noise level increased. The OSQ of the birdsong and stream sounds were similar for traffic noise, whereas the stream sound was rated higher than the birdsong for the breaker noise. The results suggest that increasing the dissimilarity in temporal structure between the target noise and natural sounds could enhance the soundscape quality. Appropriate SNRs were explored considering both PLN and OSQ. The results showed that the SNR of −6 dB was desirable when the A-weighted SPL of the noise rose to 75 dB.
19Active noise control through open windows is a noise mitigation technique that preserves 20 natural ventilation in dwellings. Designing a practical open window active noise control system 21 requires the knowledge of the physical limits on the attenuation performance. Of the numerous 22 variables to be optimised, it is the control source configuration (quantity and position) that 23 ultimately defines the maximum attenuation attainable by an active noise control system. The 24 physical limits are characterised here by systematically investigating the performance of 25 different physical arrangements of control sources, using a two-dimension simulation model 26 based on the finite-element method, which includes the diffraction effects of the window. The 27 simulations reveal that the best attenuation is achieved by placing the control sources away 28 from the edges of the window. It also shows that the plane of control sources can be placed 29 centrally with respect to the depth of the walls, for practical implementation with minimal 30 performance degradation. The simulated attenuation as a function of frequency and window 31 width, for different angles of noise incidence, can be used to provide an estimate of the number 32 of control sources, based on the desired level of attenuation. This estimate helps to determine 33 the configuration with the minimum number of control sources required for different scenarios, 34 before a more detailed system design is undertaken. 35 36
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