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Spatial Audio for Soundscape Design: Recording and Reproduction

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Spatial Audio for Soundscape Design: Recording and Reproduction applied sciences Review Spatial Audio for Soundscape Design: Recording and Reproduction Joo Young Hong 1,*, Jianjun He 2, Bhan Lam 1, Rishabh Gupta 1 and Woon-Seng Gan 1 1 School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798, Singapore; [email protected] (B.L.); [email protected] (R.G.); [email protected] (W.-S.G.) 2 Maxim Integrated Products Inc., San Jose, CA 95129, USA; [email protected] * Correspondence: [email protected]; Tel.: +65-8429-7512 Academic Editor: Gino Iannace Received: 29 March 2017; Accepted: 9 June 2017; Published: 16 June 2017 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. Keywords: soundscape; spatial audio; recording; reproduction; virtual reality; augmented reality 1. Introduction Urban acoustic environments consist of multiple types of sound sources (e.g., traffic sounds, biological sounds, geophysical sounds, human sounds) [1]. The different types of sound sources have different acoustical characteristics, meanings and values [2–4]. Conventionally, environmental noise policies are primarily centered on the energetic reduction of sound pressure levels (SPL). However, SPL indicators provide limited information on perceived acoustic comfort as it involves higher cognitive processes. To address the limitations of traditional noise management, the notion of a soundscape has been applied as a new paradigm. Schafer, a Canadian composer and music educator, introduced the term soundscape to encompass a holistic acoustic environment as a macrocosmic musical composition [5]. In this context, soundscape considers sound as a resource rather than waste and focuses on people’s contextual perception of the acoustic environment [6]. Due to rising prominence of the soundscape approach, ISO TC43 SC1 WG 54 was started with the aim of standardizing the perceptual assessment of soundscapes. As defined in ISO 12913-1: definition and conceptual framework, acoustic environment is “sound from all sound sources as modified by the environment” and the modification by the environment includes effects of various physical factors (e.g., meteorological conditions, absorption, diffraction, reverberation, and reflection) on sound propagation. This implies that soundscape is a perceptual construct related to physical acoustic environment in a place. Appl. Sci. 2017, 7, 627; doi:10.3390/app7060627 www.mdpi.com/journal/applsci Appl. Sci. 2017, 7, 627 2 of 21 acoustic environment [7]. The context includes all other non-acoustic components of the place (e.g., physical as well as previous experience of the individual). Herranz-Pascul et al. [8] proposed a people-activity-place framework for contexts based on four clusters: person, place, person-place interactionAppl. Sci. 2017 ,and7, 627 activity. The suggested framework shows interrelationships between person2 and of 22 activity and place, which may influence a person’s experience of the acoustic environment. It is evident from [8] that the human auditory process is deeply entwined in the person-activity-place framework.According Thus, to sufficient ISO 12913-1, insight the about context the plays huma an critical auditory role process in the perceptionis imperative of ato soundscape, record and reproduceas it affects an the acoustic auditory environment sensation, the with interpretation sufficient ofperceptual auditory sensation,accuracy for and proper the responses analysis. to Forthe simplicity, acoustic environment Zwicker and [ 7Fastl]. The has context grouped includes the human all other auditory non-acoustic processing components system into of two the stages: place (1)(e.g., the physical preprocessing as well in asthe previous peripheral experience system, and of the(2) information individual). processing Herranz-Pascul in the auditory et al. [8 ]system proposed [9]. a people-activity-placeCurrent reproduction framework methods for(e.g., contexts loudspeakers, based on headphones, four clusters: etc.) person, have sufficient place, person-place fidelity for properinteraction interpretation and activity. of frequency The suggested and temporal framework char showsacteristics interrelationships in the peripheral between system person (stage and 1). Asactivity the spatial and place, dimension which of may sound influence is only a person’sinterprete experienced in stage of2, thewhere acoustic there environment.is significant exchange of informationIt is evident between from [both8] that ears, the complexity human auditory of reproduction process isis deeplygreatly entwinedincreased. in For the instance, person- toactivity-place locate a sound framework. source in space, Thus, the sufficient characteristic insights of about intensity, the human phase, auditory and latency process must isbe imperative presented accuratelyto record andto both reproduce ears. Hence, an acoustic spatial environment audio recording with sufficientand reproduction perceptual techniques accuracy forshould proper be reviewedanalysis. Forin simplicity,the technological Zwicker perspective and Fastl has with grouped a focus the on human their auditoryrelationship processing with soundscape system into perception—thetwo stages: (1) themain preprocessing goal of this paper. in the peripheral system, and (2) information processing in the auditoryAs recording system [9 ].and reproduction techniques are heavily employed in the soundscape design process,Current a brief reproduction discussion methodswill shed (e.g., light loudspeakers, on the areas where headphones, such techniques etc.) have are sufficient most commonly fidelity for used.proper The interpretation soundscape design of frequency process andcan be temporal summarized characteristics into three stages, in the peripheralas illustrated system in Figure (stage 1 [10]. 1). StageAs the 1 spatial aims to dimension define and of analyze sound is existing only interpreted soundscapes. in stage In this 2, where stage, there soundscape is significant researchers exchange and of plannersinformation are between required both to ears,evaluate complexity and identify of reproduction ‘wanted issounds’ greatly to increased. be preserved For instance, or added, to locate and ‘unwanteda sound source sounds’ in space, to be the removed characteristics or reduced of intensity, based on phase, the context. and latency In Stage must 2, be soundscape presentedaccurately planning andto both design ears. scenarios Hence, spatialare proposed audio recordingbased on the and analysis reproduction of the existing techniques soundscapes. should be The reviewed soundscape in the designtechnological proposals perspective will then withbe simulated a focus on to theirbe obje relationshipctively and with subjectively soundscape evaluated perception—the by stakeholders main togoal determine of this paper. the final soundscape design. In Stage 3, the final soundscape design will be implemented in situ.As After recording implementation, and reproduction validation techniques of the soundscape are heavily design employed will be in performed the soundscape with iteration design ofprocess, Stage a1 brieffor analysis discussion of implemented will shed light soundscape on the areas design. where such techniques are most commonly used. The soundscapeThroughout designthe soundscape process can design be summarized process, soundscapes into three stages,can be asevaluated illustrated based in Figure on the1[ real10]. acousticStage 1 aimsenvironment to define or andvirtual analyze (reproduced existing or soundscapes. synthesized) environment In this stage, [6,11]. soundscape Similarly, researchers in Stage 1 (analysisand planners of existing are required soundscape) to evaluate and Stage andidentify 3 (implementation ‘wanted sounds’ of soundscape to be preserved design), or soundscapes added, and ‘unwantedcan be assessed sounds’ in real to beor removedreproduced or reducedacoustic basedenvironments. on the context. The reproduced In Stage 2, acoustic soundscape environment planning isand constructed design scenarios from areaudio proposed recordings based in on the the real analysis world. of theIf the existing physical soundscapes. location Thefor soundscape soundscape implementationdesign proposals is will not then available be simulated (i.e., not to built), be objectively future soundscape and subjectively design evaluated scenarios by might stakeholders also be evaluatedto determine using the finalsynthesized soundscape (or simulated) design. In Stageacoust 3,ic the environment final soundscape in Stage design 2 (soundscape will be implemented planning
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