Introduction
Soundscape represents a step change in the field of environmental acoustics in that it combines physical, social, and psychological approaches [
1]. Although the term soundscape was introduced in the 1960s, significant attention to it has mainly been paid in the last decade or so in the field of community noise and environmental acoustics by researchers and recently by practitioners, including policy makers.
This paper aims to explore the current situation and future challenges in soundscape. Starting with a framework on research and practical needs in soundscape and a brief introduction of some recent/current networks, activities, projects, and publications, this paper then presents a systematic review of recent progress in soundscape research and practice. A short review of the soundscape research in China is also given.
A soundscape framework
To review the existing research and explore future challenges, it is important to establish a framework about what are needed, taking into account both research and practice facets. Such a framework is proposed in Fig. 1, where five main issues are considered [
2], as discussed below.
Understanding and exchanging
There is a need to better understand the overall and diverse effects of soundscapes on citizens, in positive or negative ways. For this, several facets needed to be considered:
1) Defining the scope of soundscape definition.
2) Soundscape evaluation with interdisciplinary cross-breeding of innovative and emerging scientific concepts and methods related to the main facets of soundscape research, connecting physiologic (sensory), psychological, psycho-physical, cognitive, emotional, social, physical, and architectural approaches. It is also important to examine cultural differences.
3) Determining essential factors for soundscape description.
4) It is important to integrate the knowledge acquired from different fields into explicit modeling (physics and computational intelligence).
Collecting and documenting
Given the wide scope of soundscape, it is important to gather and maintain a repository of experimental sound data to be reanalyzed and studied from inter- and transdisciplinary perspectives. A database of questionnaires and a database of case studies would also be useful. Such databases will be an invaluable resource for scientists and practitioners for years to come, allowing effective testing of new models and insights.
Harmonizing and standardizing
1) While soundscape has been researched from a range of viewpoints, it is important to review and harmonize the current vocabulary and methodology and, consequently, develop a new set of exposure indicators to characterize sound quality of environments that improves significantly on the conventional decibel level approach that has been the basis of current European and international regulations. The indicators should be suitable to assess health related quality of life and functional health, which can then be used to evaluate claims related to health promotion benefits.
2) There is also a need to develop standard protocols, such as text and/or audio-visual documentation, which can be used to better assess cross-contextual and cross-cultural differences that may be responsible for discrepancies of study results.
3) The indicators and protocols could lay the foundations for standardization and lead to future European/international standards.
Creating and designing
1) There is a need for practical guidance in soundscape design, based on research as well as successful practical examples. It is also of significance to provide guidelines for preserving architectural heritage sites from soundscape perspectives.
2) It would be important to develop tools and corresponding software for the design and implementation of soundscapes for use by urban planners and policy makers. Auralization tools are especially relevant and important for soundscape design.
Outreaching
1) It is important to create awareness and promote communication concerning urban soundscapes and quiet areas among the policy makers and stakeholders, especially with the requirements in the EU Noise Directive (END) [
3]. It should also be recognized that soundscape studies are not only for the improvement of the current sound environment but also for the conservation of our sound environments, which can be classified as acoustic heritages.
2) It is equally important to create awareness among the general public, especially given that soundscape is relevant to a much wider range of citizens than noise.
Good soundscapes strengthen and promote the image of the city/landscape, stimulate tourism, create healthy stress releasing settings for its inhabitants, and improve social cohesion. The health, cultural, and economic benefits include the following.
① Health. Due to the increasing numbers of elderly people in the EU, there is a need to provide supportive environments that prevent the degradation of functional health. Moreover, the engagement in health-promoting activities, such as walking and running, is less likely in unpleasant neighborhoods. Furthermore, the design/redesign of well-perceived soundscapes is a prerequisite of an adequate learning environment for children to foster language and cognitive development, motivation, and social interaction.
② Culture. Soundscape is a significant factor in the ‘sensing of places’. Cities and landscapes are now becoming more and more similar in terms of their sound environment, and the diversity of sounds that distinguish and characterize places are to be lost, and therefore, the issue of maintenance and restoration of diversity of cultures and of their soundscapes is vital, also as an important dimension of tourism. Soundscape studies will help the understanding of acoustic conservation and restoration, adding a new component/dimension to the “World Heritage” concept.
③ Economy. Not only can attractive soundscapes enhance cultural identities but also economic grounds enhance property prices, create an attractive setting for economic investment, offset health costs through provision of restorative living spaces, and reduce costs caused by antisocial behaviors. Soundscape research could help prevent costly unnecessary infrastructural noise mitigating activities and provide more cost-effective solutions.
Recent activities
With the growing interests in soundscape, there have been increasing activities in the field/sector, including networks, research projects, standardization, practice, and publications. Some of the activities are reviewed briefly in this section.
UK EPSRC NoiseFutures Network
This network (http://noisefutures.org/) arises from the participation of the members in the UK Engineering and Physical Sciences Research Council (EPSRC) Ideas Factory “A Noisy Future? Making the World Sound Better.” This brought together participants from a wide range of academic backgrounds and experiences alongside contributions from policy makers and consultants. The skills and backgrounds of the participants include social science, transport engineering, traffic noise emissions modeling and 2.5D mapping, management and control of traffic noise, economics, media and cultural studies, maths, electronics, sound art, room acoustics, acoustics, building acoustics, psychoacoustics, noise control, health sciences, sound quality engineering, environmental acoustics, aeroacoustics, auditory psychophysics, structural dynamics, mechanical engineering, micro mechanics, and noise mapping. The network started from June 2006. The primary purpose of the network is to facilitate interdisciplinary (multiinterest) research on future soundscapes [
4]. More specifically, the objectives of the network are listed as follows:
1) To engage with policy makers, industry representatives, and other interested in future soundscapes.
2) To generate a suite of research proposals to EPSRC and other sponsors.
3) To expand the network to include expertise required for future research needs.
4) To build the legitimacy of the group as an advisory body.
5) To create a new research community that integrates researchers, artists, industry, educational bodies, and policy makers and enables effective communication across disciplines and sectors.
6) To explore the best methods of involving the public in research on soundscapes.
7) To raise the profile of future soundscapes in the media.
8) To encourage interdisciplinary training and information exchange for research students and research assistants in the fields.
9) To create a critical mass in the field, placing the UK in a world-leading position in research into soundscapes.
10) To encourage and deliver international collaboration.
Main activities include the following:
1) Sounder Spaces Conference, jointly organized with the Greater London Authority (GLA), 2007.
2) Low Frequency Noise Conference, jointly organized with the UK Noise Association, 2007.
3) The Future of Computational Acoustics Conference, jointly organized with the Isaac Newton Institute, 2007.
4) Tranquil Space Conference, jointly organized with the Greater London Authority, 2009.
5) UK SoundMap project, 2009.
6) Soundwalks in London and Edinburgh, 2009.
7) Workshops relating to issues in soundscape and future development, 2006-2009.
EU COST Action on Soundscape
A European Cooperation in Science and Technology (COST) Action on Soundscape of European Cities and Landscapes (http://soundscape-cost.org/) started in May 2009. The main aim of the Action is to provide the underpinning science for soundscape research and make the field go significantly beyond the current state-of-the-art through coordinated international and interdisciplinary efforts. There are five work packages, including understanding and exchanging, collecting and documenting, harmonizing, creating and designing, and outreaching and training. The Action is working on an integrated database of laboratory/field studies, harmonized/standardized soundscape assessment and indicators, academic and practical publications, and tools to support designers and decision makers in planning and reshaping urban/rural spaces. It will promote soundscape into current legislations, policies, and practice, for improving/preserving our sonic environment [
2].
Recent activities include the following:
1) Workshop on Hot Topics in Soundscapes, Edinburgh, UK, 2009.
2) Workshop on Soundscape Contributions to Standardisation, Berlin, Germany, 2010.
3) Workshop on Understanding, Modeling and Measuring Soundscapes, Gent, Belgium, 2010.
4) Conference on Soundscape Support to Sustainable Development, Stockholm, Sweden, 2010.
5) Training School on Soundscape, Lubljana, Slovenia.
International Organization for Standardization (ISO)
A working group ISO/TC43/SC1/WG54 was formed in 2008 on the perceptual assessment of soundscape quality. The scope of the Standard is to provide specifications for questionnaire studies. The Standard is primarily intended for researchers to assess perceived soundscape quality and for public users to evaluate soundscape quality in existing outdoor areas. The Standard will specify a questionnaire protocol, which includes questions on sound source identification and perceived quality of the soundscape, as well as reporting core information [
5].
In 2009, three project meetings were held in Berlin, Ottawa, and Seoul, respectively. The main themes were reaching a common understanding of the scope of the proposed standard.
Research projects
The importance of soundscape research has been recognized by governmental organizations and national funding bodies in Europe, and a number of national research projects relating to this field have been, and are being, carried out in Europe, such as two UK Noisefutures Network associated soundscape projects, namely, ‘Automated Soundscape Identification’ and ‘Positive Soundscapes Project’ (www.positivesoundscapes.org/); a number of soundscape projects supported by the Royal Society, British Academy and British Council (www.sheffield.ac.uk/acoustics); the ‘Soundscape Support to Health’ project funded by the Swedish Foundation for Strategic Environmental Research; the “Eyer-Hear Project- Qualitative Sound Maps for Visualization of the Urban Soundscapes” funded by the Portuguese Science and Technology Foundation; and a series of soundscape projects funded by the French Ministry of Town Planning, Housing, and Construction, as well as the PREDIT program (National Research Program on Innovation in Transport).
At the EU level, in the Quieter Surface Transport in Urban Areas (SILENCE) and the Quiet City Transport (QCity) projects, some subtasks relevant to soundscape, perception, acceptance, and expectation have been included, although the subjective evaluation has been limited mainly to annoyance perception. In the Coordination of European Research for Advanced Transport Noise Mitigation (CALM) network, the need for perception-related research for identifying indicators and parameters for quiet areas has been indicated. The Road Traffic and Aircraft Noise Exposure and Children's Cognition and Health: Exposure-Effect Relationships and Combined Effects (RANCH) project has considered the potential benefits of a restorative soundscape at home on children’s cognition, although the study mainly concerns the acoustic environment at home, which is only a small part of the whole soundscape picture. The Measuring the Impossible’ Network (MINET) aims at supporting the development of new methods and investigative techniques for the measurement of complex phenomena that are dependent on human perception and/or interpretation, with sound as one dimension. The European Network on Noise and Health (ENNAH) aims to produce information that is useful for the further development of the END [
3] by examining whether existing noise maps can be used to establish any adverse effects of noise on health.
In other parts of the world including Australia, Canada, USA, Japan, China, and Korea considerable attention has also been paid to soundscape research.
Policies and practice
There have also been increasing interests in the practice and policy sectors. For example, the Greater London Authority is actively promoting several practical exemplar soundscape projects [
6], and the GLA has also hosted a number of conferences/workshops relating to soundscape. The city of Berlin is promoting the soundscape research with regard to its application concerning action plans and public places, and a successful project has been completed [
7-
9]. The city of Antwerp is using a soundscape approach to improve the acoustic environment in a new development area [
10]. Stockholm is also promoting soundscape by hosting a Conference on Soundscape Support to Sustainable Development (http://soundscape-cost.org/). The above activities are closely related to the END in terms of creating quiet areas.
Soundscape approach has also been applied in preserving and restoring archeological places of great importance, such as Pompeii, in which the tourist sensation shall be globally connected to the atmosphere of the historical site [
11].
Publications
In the last decade or so, there have been a growing number of publications in the field. In the major international conferences including the International Congress on Noise Control Engineering (internoise), the International Congress on Acoustics (ICA), the International Congress on Noise as a Public Health Problem, the European Conference on Noise Control (euronoise), the International Congress on Sound and Vibration (ICSV), as well as various national conferences, such as the Acoustical Society of America (ASA) meetings, and the UK Institute of Acoustics meetings, a number of special sessions on soundscape have been organized, from a range of viewpoints including acoustic, social, psychological, physiological, linguistic, historical, and architectural aspects. In Fig. 2, it shows the number of papers relating to soundscape research and practice of internoise in recent years.
In 2006, a special issue of Acta Acustica united with Acustica (AAA) (the Journal of the European Acoustics Association) was produced on soundscape. A number of special issues relating to the soundscape area are also being planned in other journals, including Noise Control Engineering Journal (NCEJ), AAA, International Journal of Environmental Research and Public Health, Applied Acoustics, and the Open Transportation Journal (OTJ).
A systematic review of the research and practice progress
A database has been established based on a number of main conferences, including the following:
1) International Congress on Noise Control Engineering (internoise), 2004-09
2) International Congress on Acoustics (ICA), 2001, 2004, 2007
3) European Conference on Noise Control (euronoise), 2003, 2008, 2009
4) International Congress on Sound and Vibration (ICSV), 2001-09
5) UK Institute of Acoustics meetings, 2002-08 (part)
The database, currently with 1534 papers in total, was established by selecting papers from the above conference proceedings in the following categories [
12]:
6) Soundscape (currently 663 papers)
7) Sound quality (currently 280 papers)
8) Others, mainly in community noise, noise annoyance, and noise sources (currently 591 papers)
More papers are being put in the database from a range of sources including journals, reports, and other conferences. The reason for using conference papers is that soundscape covers both research and practice sectors, and conference papers would reflect the whole picture in the field. Moreover, the number of journal papers is still rather limited.
In this section, a systematic review is made based on the current database, as well as other literature wherever appropriate, in terms of the five facets discussed in Section 2.
Understanding and exchanging
Definition
Depending on the field, soundscape has been defined from different points of view, such as ecology, arts, design, and psychology. The mostly commonly recognized definition is the one listed in the “Handbook for Acoustic Ecology” published in 1978 [
13]: An environment of sound with emphasis on the way it is perceived and understood by the individual or by a society. It thus depends on the relationship between the individual and any such environment. The term may refer to actual environments or to abstract constructions, such as musical compositions and tape montages, particularly when considered as an artificial environment.
Based on intensive discussion of the ISO/TC43/SC1/WG54 working group and the COST network, at least in the context of the proposed Standard, soundscape is defined as [
14] the perceived sound environment in context by an individual, a group, or a society.
Evaluation
A key part of soundscape research is to understand how the soundscape within its proper context affects its users. With a wide range of multi- and interdisciplinary research, much work in this aspect has been carried out, both under field and laboratory conditions, considering a range of spaces and locations, sound sources, and people [
12]:
1) Spaces/functions include urban streets, urban open public spaces, parks, schools, bus stations, theme streets, cycle path, outdoor concert, racing games, archeological sites, covered spaces, underground shopping streets, as well as a range of indoor spaces. The spaces are widely distributed across the world, although the work in Europe is considerably more than that in other countries.
2) Sound sources are from noise sources including industry noise, aircraft noise, road noise, wind turbines, and amplified music to positive sounds including natural sounds and to infant cry. The effects of a number of sound source characteristics, such as low frequency components and tonal and impulsive features, have been examined.
3) People include the social and demographical characteristics that have been considered for various users, including specific groups, such as children, deaf, hearing impaired, and blind people.
While the majority of the soundscape evaluation research has been based on social and psychological approaches, limited physiologic studies have also been conducted, including the use of functional MRI (fMRI) techniques to investigate the perception of tranquility [
15] and listeners’ reaction to different urban soundscapes [
16]. In a study by Hume and Ahtamad [
17], the effects of individual soundscape elements on the subjective assessment of pleasantness and arousal were compared with associated physiologic responses including heart rate (HR), respiratory rate (RR), and forehead electromyography (EMG) levels, and some correlations have been shown preliminarily.
The interaction between acoustic and other physical environments is an essential consideration, and of various physical conditions, the aural-visual interactions have been intensively studied. Significant correlations have been found between landscape and acoustic satisfaction, between visual and acoustic satisfaction, as well as between view and quietness in choosing a living environment [
1,
12].
Linguistic analyses could be made of the semantics of the vocabularies and of discourses encountered in the diversity of studies concerned with soundscapes using verbal responses. The case of linguistic analyses of verbal content is further mandatory because of the diversity of languages in Europe. This could also reflect the cultural variations in conceptualizations and subjective responses to noise and their relations to acoustic parameters. Dubois and Catherine [
18] indicated that cognitive evaluation in the first place as a ‘prefilter’ can be used to decrease the complexity in relevant category sound identification. Payne [
19] suggested that the context, the exact situation, and the perceivers’ interpretation of sound events played a significant role in sound classification; therefore, new affectively termed categories that allow variations in the perception of sounds and context were created alongside the affective evaluation carried out by semantic different scales.
Although considerable work has been carried out in the soundscape evaluation, as discussed above, there are still recognized needs for further work [
2]:
1) Detailed knowledge on sensory perception is needed to identify features that are distinguishable by the human sensory system. Not only classical psychophysics can be useful in this respect but also recent results obtained from brain imaging.
2) The way the sensory perception is organized in objects and streams, and how this depends on personal characteristics and how attention affects the external environment is shaped internally are important research topics.
3) To discover how meaning is attached to the objects and streams formed in the human mind, within a cultural and social context, is a tremendous challenge. It relates strongly to the spearhead research on the mechanisms of thought and the working of the human mind.
4) Somewhat in parallel to the above, the effect that a stressed or harmonized human-environment relationship can have on mental health needs further investigation.
5) To optimally use the results obtained by cognitive science, brain imaging/neural imaging/neuro-informatics, and research on auditory perception, the knowledge embedded in these research communities needs to be made reachable to the community of soundscape researchers.
Description
Relating to soundscape evaluation, it is of great significance to describe soundscapes systematically, taking into account various facets in terms of space, source, people, and context/environment. Figure 3 is a possible taxonomy of the acoustic environment [
20], for sound sources. It has been constructed in terms of categories of places, indoor and outdoor, and within the outdoor environment urban, rural, wilderness, and underwater.
To investigate an existing soundscape or to design a new soundscape, it is essential to describe it in terms of designable factors. As an example, for urban open public spaces, such a system/framework is proposed, as shown in Fig. 4, where four facets are considered, namely, characteristics of each sound, acoustic effects of the space, social/demographic aspect of the users, and other aspects of the physical/environmental conditions [
21].
Within the ISO/TC43/SC1/WG54 working group, a subgroup, called ‘box group’, has been formed [
5] to establish the relationships between various facets of soundscape, including contexts, physical soundscape, soundscape perception process (psychological and physiologic), coping behavior, and outcomes [
22].
Modeling
Modeling and simulation are strong tools for helping to understand how complex systems work. A range of models are relevant here, from perception modeling, to the modeling of physical soundscape, as well as the human-soundscape interactions. Simulation tools could include computational auditory scene analysis tools, numerical ear models, saliency detection modules, cognitive mapping tools, etc. Closely relating to the soundscape modeling is sound source recognition. It is a very detailed yet extremely important facet of understanding how soundscapes are perceived and how they affect the user. There are different angles to this problem: in a physical sense, there may be an advantage in recognizing the source of the sounds as accurately as possible, but it is equally important to identify what a human listener will detect and think to recognize when exposed to the sound mixture. It is the latter that is essential as a starting point for soundscape perception modeling.
While most research relates soundscape descriptors to perception in a fashion strongly related to epidemiologic research, a bottom-up approach has been used by De Coensel and Botteldooren [
23-
24]. The individual sensory, cognitive, and emotional mechanisms that play a role in soundscape perception are discerned, and a human mimicking software model was proposed. In particular, such a model is able to reproduce and explain, in a qualitative way, trends as observed in epidemiological research on soundscapes [
25]. Since human listeners process sound as meaningful events, Niessen et al. [
26] developed a model to identify components in a soundscape that are the basis of these meaningful events. First, they selected structures from the sound signal that are likely to stem from a single source. Subsequently, they used a model of human memory to predict the location at which a sound is recorded and to identify the most likely events that constitute the components in the sound given the location. Accepted or corrected annotations can be used to improve the classification further. This speeds up the annotation process and makes it possible to annotate complex soundscapes both quickly and in considerable details [
27]. Another approach is the use of artificial neural networks, with which models have been developed to predict soundscape perception [
28].
In terms of modeling techniques for physical soundscapes and sound environments, much work has been carried out [
1,
29-
30], considering the effects of various factors, such as meteorological/atmospheric conditions and the effects of urban elements. With artificial neural networks, models have been developed to predict the level and the temporal and spectral composition of the sound pressure in urban soundscapes [
31].
Collecting and documenting
Sounds
In the Soundscape category of the database, by using keywords ‘sound database’ and ‘database of sound(s)’, four papers were found. With ‘sound recording(s)’ and ‘recording(s) of sound(s)’ as keywords, 48 papers were found. After reviewing those papers, it was found that 34 of them were related to, directly or indirectly, sound database/recordings, and among those, four papers mentioned the need for creating sound databases [
32-
35]. Sound recordings were used as one of the research methods in 30 papers. The environmental sounds of the Amazon in Brazil were recorded and proposed to be divided into three main categories: natural, technological, and anthropic environment, which could contribute to the local soundscape as well as the expression of local culture [
33]. Lemke [
36] stated that due to the absence of the visualization of the events, recording a sound from its source, which transited the ‘real thing’ into electronically created signals, changed the physicality of the sound, and made it difficult to identify. Therefore, he collected and archived sounds by means of drawing, writing, and photography and sound recording. Brambilla et al. [
37] employed both site binaural recordings and photos to collect the data of 12 sites and confirmed the important roles of auditory perception and visual information on the assessment of a site through the laboratory listening tests. Overall, although some initial databases have been, and are being established, and discussion has been made about the ways of establishing sound archives in soundscape research [
38], more systematic work is still needed.
Questionnaires
Questionnaire survey is a commonly used method in soundscape research, and a considerable number of questionnaires have been developed in different studies [
1], and correspondingly, a large amount of survey data has been collected. In an EU study, over 10000 questionnaires have been distributed with simultaneously measured sound level, and correspondingly, acoustic models for microscale urban areas have been developed to obtain sound map data of the case study sites. In Italy, experimental studies have been carried out using sound measurements, binaural recordings, and interviews, in a range of sonic environments including nine urban parks, a rural area, 12 squares, and the outdoor archeological area of Pompeii. There have been three Flemish noise surveys at home on annoyance, each with 3000-5000 samples, where an advantage is that many data are geographically referenced, and many Geographic Information System (GIS) layers are coupled. The “Maglev field experiment” was conducted in a house with traffic sound playback. A series of studies in Berlin generated soundscape data combining physical, psychoacoustic, and perceptive measurements in different residential areas. Macro- and microscopic approaches were chosen for sound walks, environmental screening, acoustic measurements, and narrative interviews. The data collection is available in raw data and triangulated data concerning the combined approach. In France and other countries, a large number of urban squares have been surveyed, with questionnaires and aural-visual recordings [
2].
Case studies
A number of practical soundscape projects have been carried out, as also discussed in Section 3.5. In the case of Alcântara bridge in Lisbon, a noisy urban place, the soundscape approach was applied as an alternative solution for simple noise reduction, through the use of masking effects of the natural soundscape and an electro-acoustic system that reinforces the natural soundscape [
39]. In Korea, the soundscape was designed for a memorial space with a seaside view [
40].
Needs for collecting and documenting
Overall, the amount of soundscape data and the number of case studies using the soundscape concept for improving the living environment is steadily growing. However, ongoing soundscape researches have different approaches. In the same time, new techniques for assessing soundscape quality and new theories are being designed and invented. It remains however rather difficult to test new theories on available data. It is therefore important to make the body of existing data available to all researchers in the field, preferably in comparable formats, for testing their theories and ideas. It is expected such databases will stimulate researchers to start meta-analyses on the collected materials, which will strongly increase the statistical strength of the resulting conclusions.
For establishing such databases, it is important to determine what data should be included. The data could take very different forms: audio-visual recordings, interviews, tables obtained from social surveys, acoustic measurements with different equipment and procedures, etc. It is also useful to explore the synergies and differences [
2]:
1) Between cities and landscapes, given their considerable differences, for example, aural-visual interactions would be rather different in the two settings;
2) between field studies and experimental settings, given that in the latter many other sensory factors are not included; and
3) between verbal data collection and analysis and physical measures, which have been paid different attention by researchers in different disciplines.
Harmonizing and standardizing
Indicators
Efforts have been made to derive certain indicators, in a number of rather different ways, for the evaluation and design of soundscapes. Raimbault et al. [
41] explored common factors in the identification of urban soundscapes through pilot studies in two French cities. Botteldooren [
42] proposed to use fuzzy noise limits. Pheasant et al. [
43] derived formulas to calculate tranquility rating, which depends on the sound pressure level and the percentage of natural features contained within a scene [
44]. Davies et al. [
45] suggested to measure and map soundscape speech intelligibility. Woloszyn et al. [
46] used geospatial knowledge modeling and representation techniques, leading to a methodology for semantic integration of the urban ambient soundscape model, namely, integrating psychophysical information into a powerful geocomputational basis for pedestrian acoustic exploration of a city. Hiramatsu et al. [
47] explored environment similarity index concerning sonic environment toward the evaluation of sonic environment. Licitra and Memoli [
48] proposed noise Indicators and hierarchical clustering in soundscapes.
However, there is still a need to derive/examine/harmonize soundscape indicators, based on multidisciplinary analysis of various physical, psychological, social, and physiologic parameters, by coupling physical parameters with, for example, semantic analysis of verbal data collected from a diversity of techniques. These parameters could be integrated into indicators through statistical methods as well as cognitive modeling using artificial neural networks [
28] or symbolic representations developed in sound recognition research. It is important to seek the synergies of different definition/understanding of soundscape from different disciplines/sectors, defining a “common language.” Indeed, multisectoral environmental health impact assessment [
49], preservation of quiet areas, and the design of ‘supportive environments’ require new insights into the existing annoyance data and new integrative research strategies. Within this context, the appropriateness of health and Quality of Life outcome indicators should be assessed and summarized, and a required set of moderator/mediator variables should be proposed [
2]. In the above, the acoustic properties of environmental noise have to be considered and combined with the empirical data. Soundscape indicators could take the form of a single index, or a set of indices, corresponding to different facets of soundscapes.
Protocols
Corresponding to the soundscape indicators, it is important to develop standard protocols for describing and evaluating a soundscape, and also for assessing cross-cultural and cross-contextual differences. Physical measure of soundscapes is another important dimension, for the application and calculation of soundscape indicators, for understanding the human-environment relationships, and for validating relevant simulation/modeling. It is important to deal with applicable measurement procedures with respect to a balance between scientific accuracy and practical applicability, also considering comparability and reproducibility [
2].
Standardisation
Along with the standard protocols is the standardization. While it is argued that standardization could restrict the creativity in designing soundscapes, from a planning point of view it is very useful to have standards. They are not necessarily used to rank different soundscapes, but at least they can provide a standard way of describing and integrating various key factors. The proposed standard on the perceptual assessment of soundscape quality would be a starting point on this [
5] (also see Section 3.3).
Creating and designing
Design guidance
The development of design guidelines and good practice guidance would be vital for the implementation of soundscape research. In the Soundscape category of the database, by using keywords ‘design guideline’ and ‘design guidance’, eight papers were found, although only four were actually relevant [
39,
50-
52]. Based on the investigation of the physical acoustic parameters and human perception in the landscape that is exposed to the traffic noise in Hong Kong, it was indicated that the results could be useful for the design of recreational parks in terms of soundscape design guidance [
50]. Kang [
52] demonstrated the design potentials considering four key components, namely, sound, space, people, and environment, and introduced initial planning and design guidelines for urban open public spaces.
Overall, while currently soundscape is mainly a research subject, the practical implementation will need significant attention. There is still a need for a systematic examination of the effectiveness of design changes, in terms of planning, landscape, architectural elements, and sound components, on the creation and improvement of soundscapes, including not only the acoustic aspect but also people’s perception. Both urban and rural soundscapes need to be considered. Associated with the design guidelines, good examples of practical projects are needed. While soundscape research has mainly been for outdoor spaces, the methods may also be applicable for enclosed spaces having a function similar to urban spaces, such as commercial and entertainment areas, shopping malls, airports, and train stations, where the acoustic comfort and sound quality cannot be dealt sufficiently only with noise parameters as is in the current practice. Although the acoustic comfort evaluation has been carried out in a range of architectural spaces, design guidelines in terms of acoustic comfort are still rather limited. Another important application of soundscape research is the acoustic preservation of architectural/landscape heritages.
Design tools
Efforts have been made in developing tools to aid design, from various points of view. Davies et al. [
53] suggested an evaluation tool, integrating perceptual results with outlines of what can be measured and how user behavior can be characterized to supply the information that an urban design or planning team might need. Fiebig and Genuit [
54] proposed a synthesis tool to derive psychoacoustic maps, which could improve the planning reliability in the context of the redesign of cities and their road traffic situations. Bunting et al. [
55] suggested an instrument that would be capable of characterizing a sound field in terms of the relative contributions of different noise sources, along with the technological advancements in microelectronics and continuing research into signal characterization and classification techniques. A design tool, Trans-Acousmatic Design, with two main concepts of metabolic effect and acousmatics, was used in the research project of Acoustic Design Artifacts and Methods for Urban Soundscapes, and a sound-art installation was proposed to be employed in the examination of the masking effect in this project in order to mask unwanted sounds in a park [
56].
Yu and Kang [
28] developed a tool to predict the subjective evaluation of soundscape quality by potential users using known design conditions, such as physical features of a space, acoustic variables, and characterizes of the users. Models of predicting soundscape quality, including sound level and acoustic comfort evaluation, have been developed using artificial neural networks as well as the ordinal logistic regression (OLR) technique, respectively. Since there are considerable differences in soundscape evaluation between various case study sites in terms of the effects of various factors, it is necessary to classify urban open spaces into typical categories and develop submodels for each category. In another study, a neural network classifier as a design tool for city planners, architects, and materials producers was utilized in a diagnostic system for soundscape certification, including green labeling of soundscapes, and a database was created from the sounds of four urban residential areas [
35].
To aid urban soundscape design as well as for public participation, it would be useful to present the 3D visual environment with an acoustic animation/auralization tool, where considerations should be given to various urban sound sources, dynamic characteristics of the sources, and the movements of sources and receivers. The calculation speed should be reasonably fast, so that a designer can adjust the design and then immediately listen to the difference. A key issue of achieving fast acoustic animation/auralization for urban soundscape is to simplify the simulation algorithms while retaining reasonable accuracy [
52]. Since human sensitivity to a particular sound source might be reduced within a complex sound environment with multiple and moving sources, to provide a fast urban acoustic animation/auralization, simplifications of calculation parameters have been explored through a series of subjective experiments [
57].
Overall, although some initial tools and guidance have been developed, there is still a great need to improve them, based on the EU COST workshop on Hot Topics in Soundscapes, Edinburgh, 2009 [
14]. It was discussed that there are different needs for different users in terms of tools for soundscape design:
1) Planners need different tools at different stages in the planning process, such as master plan, detailed plan for the development of an area, and the evaluation of results. For the master plan, the planners need categories of soundscapes, organized according to the intended use of an area, and the kind of sounds that may be heard. The categories may be used in a geographical information system (GIS) to provide an overview of a geographical region. In a detailed plan for the development of a local area, the planners need a screening tool to see when and where soundscape can be of use. The planners need tools for determining the acoustic objectives for the area and tools for design, namely, what physical aspects to modify in order to meet the acoustic objectives.
2) The consultants need high-quality survey techniques, simulation tools (improved noise maps involving listening to simulated soundscapes), tools for measuring people’s perceptions of soundscapes, reliable tools that describe what sounds people hear at a place, and models/tools to predict people’s perceptions of planned soundscapes.
It was also clear from the workshop that there is no single recipe, there are several layers (inheritage, uses, and purposes), and consideration should be given to the plurality of point of views (e.g., park is ‘place’, and the recreation area is ‘use’).
Outreaching
Policy makers
One of the major drivers for the recent intensive soundscape research and practice is the need to create quiet areas according to the END [
3,
58]. Although much work has been carried out in terms of describing and evaluating soundscapes, there is still a recognized need to integrate soundscape results into policy [
59]. For this, it is important to have a series of practical indicators and design guidance and tools, as discussed in Sections 4.3 and 4.4. More effort also needs to be made to disseminate the results to policy makers. Successful examples are required to underline significant points, such as simplicity, reduction of social costs, and people’s acceptance. Attention should be paid to a wide range of applications in terms of policy making, including preservation of heritage sites [
11]. Indeed, while in the noise control sector, a basic difficulty is that no single technological fix could solve the problems on emission and immission aspects [
60]. Such multisectoral efforts are even more important in soundscape approaches. Noise maps, and further soundscape maps, could be powerful tools not only for disseminating the results of sound evaluation but also for the decision making in sound environment policy [
61-
63].
General public
With regards to policy making, there is also a need to disseminate the soundscape concept and benefits to the general public, based on much work in community noise sector [
64-
65]. The general public would need to understand how to manage the soundscape more effectively and how to complain about a negative impact. Educational programs are also needed for the general public, for their benefits and for influencing the politicians. Tools are useful to enable the users to structure their experiences of the soundscape in order to provide information to decision makers [
14]. Under the soundscape COST Action, an awareness day, on ‘Listen your city’, is planned to address the community.
Soundscape research in China
Along with the increasing attention to soundscape by the acoustic research community in Europe since about a decade ago, soundscape has also been introduced to China [
66-
70]. A number of studies have been carried out in the field, mainly by researchers in architecture and related fields, but the practical application of soundscape research has yet to begin due to the lack of political drivers like the END [
3] in Europe.
Li [
68] attempted to introduce the soundscape concept to the general public. He also collected a number of sound files, aiming at establishing a sound database. Using a computer, Li searched and classified various sounds in one of the most classic Chinese novels, The HongLouMeng (The Dream of The Red Chamber), and demonstrated the wide range of sound types in Qing dynasty [
71].
Yuan and Wu [
72] systematically explored the differences between the soundscapes in traditional Chinese gardens and the modern western soundscapes. From the perception and humanity viewpoints, the philosophy for creating landscapes and soundscapes in traditional Chinese gardens was discussed. Chen [
73] classified the soundscapes in traditional Chinese gardens into four types, namely, using meteorological conditions, using water, using animal and insect sounds, and using human activities. The importance of considering the relationships between sounds, users, and spaces was also discussed.
Ge et al. [
74] discussed the application of soundscape concept in urban landscape design, at various levels, from urban planning to the use of acoustic devices. They also carried out a number of soundscape surveys in parks [
75]. Ma and Wang [
76], based on a series of field surveys in different types of urban parks, as well as laboratory listening tests, explored the relationships between the sound pressure level and the acoustic preference of various natural and artificial sound sources. Kang and Zhang [
77–
78] also carried out field surveys in a number of urban open public spaces in China, as part of a cross-cultural comparison of urban soundscapes between China and Europe [
79].
Tai [
80] carried out a series of field surveys in urban residential areas and studied the preferences of various typical sounds in such areas, where the semantic differential technique was applied and four factors were derived, namely, comfort, space, sound source, and dynamics. Wu [
81] studied the soundscape in a residential area at the Zhejiang University and examined the sound evaluation of different user groups. Currently, a research project is on-going on the soundscapes in residential areas in China based on integrated environmental performance, aiming at developing a framework of soundscape research in China [
82].
A number of studies have been carried out on the soundscape of underground shopping streets [
83-
84], based on large-scale surveys on the acoustic comfort evaluation as well as sound preference. Correlations between sound fields and subjective evaluations have been explored, and cross-cultural comparisons have also been made [
84].
Zhao [
85] carried out some basic research about soundscape preference, especially in terms of frequency components. Currently, a research project is on-going on introducing psychoacoustics into urban soundscape research [
86].
Conclusions
While there is a tendency from purely reducing noise level to overall soundscape design, the complexity as well as potentials of soundscape research and practice has been demonstrated through systematically examining the current situations in this paper. Although considerable work has been carried out, further research is still needed in more facets, and practical implementation of the research work is yet to start. The current research works in soundscape are still at the stage of describing and identifying the problems, and they tend to be fragmented and focused on only a few special cases, e.g., based on common sense categorization of soundscapes and on local interests, such as evaluation of soundscapes especially for residential areas. A number of issues need to be addressed, such as those listed as follows:
1) While in the paradigm shift, from noise control to soundscape design, a vital step will be the explicitation, comparison, and evaluation of methods and indicators from different scientific domains in order to model soundscapes in their globality. There is currently a lack of standardization and explicitation in the categorization and measurement procedures, and there are few tools.
2) Relationships between subjectively assessed “acoustic quality of the environment” and perceived health-related quality of life and functional health are yet to be established.
3) The importance of quiet areas within reach is recognized by the EU, but no clear definition is given and there is no method by which “good” or “restorative” sound environments can be measured. For that, great effort is still needed to integrate soundscape research into practice and policy making.
Higher Education Press and Springer-Verlag Berlin Heidelberg
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