Urban Soundscape Fundamentals – Acoustics Group

Abstract

The urban soundscape, defined as the acoustic environment as perceived, experienced, and understood by people in context, represents a critical dimension of urban life with profound implications for health, well-being, and quality of life. This review provides a comprehensive introduction to the field of urban soundscape studies, specifically tailored for emerging PhD researchers. It traces the historical evolution of the concept from its roots in noise control engineering and acoustic ecology, pioneered by figures like Southworth and Schafer, to its maturation into a standardized, interdisciplinary field under the ISO 12913 framework. Key theoretical concepts and terminology, including keynote sounds, sound signals, soundmarks, pleasantness, and eventfulness, are defined and contextualized. The review details the primary objective methodologies employed for soundscape assessment, encompassing traditional acoustic parameters (e.g., Leq, Lden), psychoacoustic metrics (e.g., loudness, sharpness), spectral analysis, and advanced machine learning techniques for sound source identification. Complementing these are the subjective methodologies, including soundwalk protocols, questionnaire design using semantic differential and Likert scales, and laboratory-based listening tests, including the use of virtual reality. The established and emerging impacts of urban soundscapes on human health (stress, sleep, cardiovascular health) and overall well-being (perceived safety, restoration, quality of life) are analyzed, highlighting both the detrimental effects of noise and the restorative potential of positive soundscapes. The crucial role of perception is explored, examining individual differences (e.g., noise sensitivity, personality, demographics, expectations) and cultural variations that shape how sound environments are experienced, alongside the influence of context and multisensory interactions (particularly audiovisual). Furthermore, the review examines the integration of soundscape principles into urban planning and design, showcasing case studies and identifying strategies such as sound source management, acoustic zoning, and participatory approaches involving citizen science. Finally, it summarizes the current challenges, limitations, ongoing debates, emerging technological and methodological trends (e.g., AI, VR, multisensory assessment, citizen science), and future research directions within this dynamic field. This review aims to equip new researchers with a foundational understanding necessary to navigate and contribute to the advancement of urban soundscape studies.

I. The Evolving Concept of the Urban Soundscape

A. Introduction: Defining the Field

The sounds that envelop us in cities – the distant hum of traffic, the chatter of pedestrians, the chime of a clock tower, the rustle of leaves in a park – collectively form the acoustic environment. However, the way individuals and communities perceive, experience, and understand this environment, within the context of their activities, culture, and personal history, constitutes the urban soundscape.¹ This concept, formally defined by the International Organization for Standardization (ISO) as the “acoustic environment as perceived or experienced and/or understood by a person or people, in context” ³, marks a fundamental departure from earlier approaches that focused solely on the physical measurement of sound. It emphasizes that the soundscape is not merely the sum of physical sound waves but a perceptual construct, deeply intertwined with human experience.¹

The study of urban soundscapes is inherently interdisciplinary, drawing knowledge and methodologies from diverse fields such as acoustics, environmental psychology, sociology, urban planning and design, acoustic ecology, geography, and public health.² It requires bridging the gap between objective descriptions of sound (studied in acoustics and signal processing) and subjective sensory experiences and collective representations (studied in psychology, anthropology, and sociology).² In recent years, the field has moved towards transdisciplinarity, recognizing the need to involve not only academic researchers but also various stakeholders, including urban decision-makers, professionals of the built environment, and citizens themselves, in shaping urban sonic environments.²

This review aims to provide a comprehensive introduction to the multifaceted field of urban soundscape studies, specifically for new PhD researchers. It will trace the historical development of the concept, define key terminology and theoretical frameworks, explore the methodologies used for assessment, analyze the impacts on human health and well-being, delve into the complexities of perception, examine its integration with urban planning, and outline the current challenges and future trajectories of this rapidly evolving discipline.

B. Historical Roots: From Noise Control to Acoustic Ecology

The journey towards understanding the urban soundscape began not with an appreciation of sound, but with a concern about its negative counterpart: noise. For much of the 20th century, the dominant approach to managing environmental sound was noise control engineering, which focused primarily on quantifying and reducing sound pressure levels (SPL) perceived as unwanted or harmful. This perspective treated sound largely as a waste product to be minimized.

The intellectual seeds for the soundscape concept were sown in the late 1960s. Michael Southworth, then a PhD student in city planning at MIT, published a seminal paper in 1969 based on his 1967 Master’s thesis, “The sonic environment of cities”.¹ Southworth was among the first to use the term “soundscape” in an academic context, arguing for the importance of the sonic environment in urban perception and planning, moving beyond simple noise abatement.²

Simultaneously, and independently, the concept gained significant momentum through the work of Canadian composer, educator, and environmentalist R. Murray Schafer at Simon Fraser University.¹ Schafer and his colleagues established the World Soundscape Project (WSP) in the late 1960s and early 1970s.¹ Motivated by the perceived degradation of acoustic environments due to industrialization and urbanization – what Schafer termed “sonic imperialism” ⁹ – the WSP aimed to draw attention to these changes and advocate for a more conscious approach to listening and sonic design.² Schafer defined the soundscape broadly as “any acoustic field of study,” encompassing musical compositions, radio programs, and acoustic environments.⁶ The WSP, comprising composers and researchers like Hildegard Westerkamp and Barry Truax, undertook detailed studies, notably of Vancouver’s soundscape ¹, and developed a social and cultural approach to understanding sound environments.² They championed practices like “ear cleaning” (attentive listening exercises) and “soundwalks” (guided listening excursions) to counter habituated non-listening and promote awareness.¹⁰ Their work also emphasized the importance of documenting and preserving unique and endangered soundscapes, particularly traditional and natural ones.⁶

The emergence of the soundscape concept represented a significant paradigm shift away from the purely negative and reductionist view inherent in noise control.¹⁰ By the 1990s, researchers and practitioners in environmental noise management began recognizing the limitations of simply reducing decibel levels.² Despite technological efforts and regulations leading to lower average sound levels in some areas, noise complaints often continued to rise, indicating that physical metrics like Leq (equivalent continuous sound level) were insufficient to capture the overall quality of auditory experience or predict human response accurately.² The soundscape approach offered a more holistic perspective, considering sounds as potential “resources” – elements that could contribute positively to the environment and human experience – rather than simply “waste” to be eliminated.¹³ This shift placed the listener and their perception at the center of the investigation.²

Schafer’s work and the WSP are also widely regarded as foundational to the field of Acoustic Ecology, defined as the study of the relationship, mediated through sound, between human beings (and other living organisms) and their environment.⁸ Acoustic ecology examines the sounds of the environment (geophony, biophony, anthrophony) and how they interact and shape ecological processes and human culture.⁹ The World Forum for Acoustic Ecology (WFAE), established in 1993 with Schafer’s involvement, institutionalized this field, bringing together an international community interested in the social, cultural, and ecological aspects of sound.⁹ The journal Soundscape, published by the WFAE, serves as a key platform for communication in this interdisciplinary domain.² While closely related, some researchers distinguish acoustic ecology, which may focus more on specific species or natural systems, from soundscape ecology, which often takes a broader, landscape-level view encompassing all sound sources, including human-generated ones (anthrophony).¹⁷

Another crucial related field is Psychoacoustics, the scientific study of sound perception – how physical sound stimuli are processed by the auditory system and interpreted by the brain.¹⁵ Psychoacoustics investigates relationships between physical sound properties (like frequency, intensity, temporal structure) and subjective sensations (like pitch, loudness, timbre, roughness).²¹ This field provides essential tools and concepts for understanding the perceptual component of the soundscape, bridging the objective acoustic environment and the subjective experience.¹³ It has been instrumental in developing metrics beyond simple SPL that better reflect human auditory perception and contribute to a more nuanced evaluation of sound environments.¹⁵

The historical trajectory from noise control, focused on physical reduction, through the culturally and ecologically rich explorations of Schafer and the WSP, to the perception-centered definition now widely adopted, reveals a fundamental shift in understanding environmental quality. It mirrors broader trends in environmental science and urban studies that increasingly recognize the importance of subjective experience, perception, and human well-being alongside objective physical measures. This evolution underscores the inadequacy of purely technical solutions for complex environmental issues involving human perception and highlights the need for holistic, context-dependent approaches.

C. Maturation and Standardization (1990s – Present)

Following the foundational work of the 1970s and 80s, the 1990s witnessed the international expansion and diversification of soundscape research. Initiatives emerged across the globe, including pioneering research in France bringing together acoustics, architecture, and urban planning, and the development of the Soundscape Association of Japan under Keiko Torigoe, a former student of Schafer.² The establishment of the WFAE in 1993 further solidified an international community focused on the social, cultural, and ecological dimensions of sound.² These efforts increasingly emphasized qualitative approaches and the need for interdisciplinary collaboration to understand the diverse experiences of people in their sonic environments.²

The 2000s marked a period of consolidation and growing academic recognition. Soundscape sessions became regular features at major acoustics conferences, and dedicated special issues appeared in scholarly journals.² A distinct scientific community emerged, particularly active in Europe, Asia, and North America.² Significant impetus came from initiatives like the European COST Action TD0804 “Soundscape of European Cities and Landscapes” (active 2009-2013), which fostered interdisciplinary networking and research.²

A pivotal development was the establishment in 2008 of the International Organization for Standardization (ISO) technical committee working group ISO/TC 43/SC 1/WG 54, tasked with standardizing soundscape concepts and methodologies.¹ This led to the publication of the ISO 12913 series, the first international standards dedicated to soundscape.¹

ISO 12913-1:2014 (Acoustics — Soundscape — Part 1: Definition and conceptual framework) provided the internationally agreed-upon definition of soundscape (“acoustic environment as perceived or experienced and/or understood by a person or people, in context”) and established a conceptual framework.¹ Crucially, it formalized the distinction between the acoustic environment as a physical phenomenon and the soundscape as a perceptual construct, influenced by context.¹ This standard aimed to provide a common language and conceptual basis for communication across disciplines.³⁰
ISO/TS 12913-2:2018 (Acoustics — Soundscape — Part 2: Data collection and reporting requirements) is a Technical Specification (TS) outlining methods for collecting soundscape data, particularly subjective data from individuals.¹ It includes protocols for questionnaires, soundwalks, and interviews (Methods A, B, C) and requirements for reporting.²⁷ Recognizing the diversity of approaches, it recommends using multiple methods (triangulation) rather than prescribing a single reference method.³
ISO/TS 12913-3:2019 (Acoustics — Soundscape — Part 3: Data analysis) provides guidance and requirements for analyzing data collected according to Part 2, including methods for analyzing perceptual attributes like pleasantness and eventfulness.¹

The development of these standards, alongside large-scale international projects like the “Sounds in the City” partnership ², reflects the field’s maturation. Since the 2010s, there has been a significant increase in soundscape publications and research activity globally.² The field continues to evolve, grappling with the complexities of perception, context, and the challenges of translating research into effective practice.²

The inherently interdisciplinary nature of soundscape studies, drawing from acoustics, psychology, sociology, urban planning, geography, and ecology, is a defining characteristic.² While this brings richness and diverse perspectives, it also presents challenges in bridging different epistemologies, methodologies, and specialized vocabularies.³⁸ Standardization efforts like ISO 12913 aim to foster a common ground ³⁰, but effective communication and integration across disciplinary boundaries remain crucial for the field’s continued progress and practical impact.³⁸ New researchers entering this field must therefore be prepared to engage with diverse literature, embrace interdisciplinary collaboration, and navigate these communication challenges. Understanding the historical context—the shift from noise control, the influence of acoustic ecology, the development of key concepts, and the drive towards standardization—provides a vital foundation for appreciating the current state and future potential of urban soundscape studies.

II. Foundational Concepts and Terminology in Soundscape Studies

A clear understanding of the core concepts and terminology is essential for navigating the field of urban soundscape studies. These terms have evolved, reflecting the field’s development from qualitative, ecological descriptions to standardized, perception-focused frameworks.

A. Schafer’s Foundational Typology (WSP)

R. Murray Schafer and the World Soundscape Project introduced a highly influential typology for analyzing the components of an acoustic environment, emphasizing their ecological and cultural significance.⁶ These terms remain valuable for qualitative description and understanding the character of a place:

Keynote Sounds: These are the ubiquitous, background sounds that, while often not consciously perceived, act as the “anchor or fundamental tone” of a soundscape.⁶ They shape the overall character and are pervasive, like the key in a musical piece.⁴¹ In urban settings, the constant hum of traffic is often cited as a keynote, though Schafer considered it an unhealthy one.⁶ Other examples might include the sound of the wind in a particular location or the distant sound of industry. Keynotes provide the context against which other sounds are heard.⁴²
Sound Signals: In contrast to keynotes, sound signals are foreground sounds that are listened to consciously and typically convey specific information or demand attention.⁶ They often function as warnings or calls. Urban examples include sirens, alarms, horns, whistles, and church bells calling worshippers.⁶
Soundmarks: Analogous to visual landmarks, soundmarks are sounds that are unique and characteristic of a specific place or community.⁶ They possess a cultural significance that makes the acoustic life of that community distinct.⁶ A sound that functions as a signal (like a bell) can evolve into a soundmark if it acquires special meaning for the community, such as the iconic Big Ben chimes in London.⁶ Schafer argued that soundmarks deserve protection due to their role in defining acoustic identity.⁶ Key characteristics contributing to a soundmark’s uniqueness might include its identifiability in time and location.⁴³
Sound Event: This term refers to an individual, identifiable sonic occurrence within the soundscape, often characterized by a distinct beginning and end.⁴² Sound events can be foreground or background elements and are often the focus of perceptual analysis or listening exercises.¹¹ Examples range from a brief bird call or a car passing to more extended events like a conversation, construction activity, or a musical performance.¹¹

B. Perceptual Dimensions and Attributes (ISO Framework and Related Concepts)

As the field moved towards standardization and a greater focus on quantifiable perception, concepts derived from psychology and psychoacoustics became central, particularly within the ISO 12913 framework.

Acoustic Environment vs. Soundscape: The cornerstone of the ISO framework is the distinction between the acoustic environment – the totality of sound from all sources as modified by the environment (a physical phenomenon) – and the soundscape – the acoustic environment as perceived or experienced and/or understood by people, in context (a perceptual construct).¹ This distinction underscores that the human experience of sound is mediated by perception and context.
Perceived Affective Quality (PAQ): This refers to the emotional or affective response evoked by a soundscape. Research has sought to identify the fundamental dimensions underlying these responses.
The Circumplex Model: A widely adopted model for representing PAQ is the circumplex model, adapted from Russell’s model of affect.⁴⁵ It typically organizes affective responses along two primary, orthogonal dimensions ³⁰:

Pleasantness (Valence): This dimension captures the hedonic tone of the experience, ranging from positive (pleasant, calm, relaxing) to negative (unpleasant, annoying, stressful).³⁰ Research consistently shows that natural sounds (water, birdsong) tend to be perceived as pleasant, while technological sounds (traffic, industrial noise) are often perceived as unpleasant.⁴⁷
Eventfulness (Arousal): This dimension reflects the perceived level of activity, dynamism, or stimulation within the soundscape.³⁰ It ranges from high activity (eventful, vibrant, lively, exciting, chaotic) to low activity (uneventful, monotonous, calm). The interpretation of eventfulness can vary; for instance, a vibrant soundscape might be associated with human activity in some cultures but natural sounds in others.⁴⁷
These two dimensions define a two-dimensional space where different soundscape characters can be mapped. For example, a calm soundscape is typically high in pleasantness and low in eventfulness, while a chaotic soundscape is low in pleasantness and high in eventfulness.³⁰

ISO 12913 Attributes: Based on empirical research underpinning the circumplex model ⁴⁹, ISO/TS 12913-2 and -3 recommend using eight specific perceptual attributes (PAQs) for assessment, typically rated on Likert scales ³⁴: Pleasant, Annoying, Eventful, Uneventful, Vibrant, Monotonous, Calm, Chaotic.³⁰ These attributes are considered to represent key points around the pleasantness-eventfulness circumplex.³⁰
Acoustic Comfort: This term relates to the degree to which an acoustic environment is perceived as acceptable or satisfactory, often implying the absence of disturbance and the presence of pleasantness.⁴ While closely linked to pleasantness, some researchers distinguish it from broader soundscape evaluation, suggesting comfort might be a prerequisite or component, but not the entirety, of a positive soundscape experience.³⁶ It represents a goal that transcends simple noise reduction, aiming for positive or agreeable acoustic conditions.³⁰
Other Relevant Concepts: While pleasantness and eventfulness are dominant, other perceptual dimensions are sometimes discussed or measured, including:

Familiarity: How usual or common a soundscape or its components are perceived to be.⁴
Appropriateness/Congruence: The perceived suitability or consistency of the soundscape with the place, activity, expectations, or visual context.⁴
Informational Capacity: The degree to which the soundscape provides useful or meaningful information.³⁰

The evolution from Schafer’s ecologically grounded terms to the perception-focused ISO dimensions reflects a necessary progression in the field. Schafer’s typology offers rich descriptive power, vital for understanding the unique character and cultural meaning embedded in specific soundscapes.⁶ However, their qualitative nature makes quantification and comparison across diverse contexts challenging. The ISO framework, rooted in psychological models of affect, provides standardized dimensions (Pleasantness, Eventfulness) and attributes that can be measured using validated scales.³⁰ This standardization facilitates quantitative analysis, modeling, comparison across studies, and ultimately, integration into policy and planning processes.¹ Yet, this gain in standardization and comparability potentially comes at the cost of reducing the complexity and nuance captured by earlier, more qualitative approaches.⁶ Researchers must be mindful of this trade-off, selecting terminology and frameworks appropriate to their specific research questions, whether focused on deep qualitative understanding or broader quantitative comparison and prediction.

C. Critiques and Nuances

Despite the growing consensus around the ISO framework, the concept of soundscape is not without its critics and ongoing debates. Anthropologist Tim Ingold, for example, critiqued the very analogy of “scape” (as in landscape) for sound, arguing that sound is fundamentally more dynamic, temporal, and embodied than static visual landscapes suggest.⁶ He proposed that our experience of sound might be better compared to experiencing the weather – immersive and ever-changing – rather than surveying a fixed geography.⁶

Furthermore, the widespread adoption of the term “soundscape” across various disciplines has led to differing uses, some of which deviate from the perception-centered ISO definition.²⁰ In fields like ecology or underwater acoustics, “soundscape” is sometimes used synonymously with the acoustic environment itself, focusing on the collection of sound sources (biophony, geophony, anthrophony) rather than human (or animal) perception in context.¹⁷ This divergence highlights an ongoing tension between the human-centered approach codified by ISO and broader ecological or physical acoustic perspectives.

Additionally, while the Pleasantness-Eventfulness model provides a useful framework, reducing the complex, multifaceted human experience of sound environments to just two primary dimensions may be an oversimplification.⁵⁵ Other factors like perceived control, meaning, memory, and cultural significance play vital roles but may not be fully captured within this model alone.

D. Insights and Implications from Concepts and Terminology

The terminology used in soundscape studies reflects the field’s journey and its core tenets. The fundamental distinction between the acoustic environment (the physical sound waves) and the soundscape (the perception of those waves in context) is paramount.¹ This distinction justifies the entire soundscape paradigm, moving beyond the purely physical measurements of noise control to embrace subjective human experience. It necessitates the use of both objective methods (to characterize the acoustic environment) and subjective methods (to assess the soundscape), and drives research aimed at understanding the complex relationship between the two.¹³ Understanding this core distinction is crucial for any researcher entering the field.

The coexistence of Schafer’s qualitative terms (keynote, signal, soundmark) and the ISO’s quantitative dimensions (Pleasantness, Eventfulness) highlights a key dynamic in the field: the balance between descriptive richness and measurable standardization. New researchers should appreciate the value of both approaches and select their conceptual tools based on their research aims.

Table II.1: Comparison of Key Soundscape Terminologies

Term	Originator/Framework	Definition	Example/Application
Acoustic Environment	ISO 12913-1	Sound from all sound sources as modified by the environment (Physical phenomenon) ¹	The measurable sound pressure levels, frequencies, and sources present at a location.
Soundscape	ISO 12913-1	Acoustic environment as perceived or experienced and/or understood by a person or people, in context ¹	How a person feels about the sounds in a park (e.g., peaceful, annoying) based on the sounds, visuals, activity.
Keynote Sound	Schafer/WSP	Pervasive background sound, often unnoticed, setting the environment’s character ⁶	Continuous traffic hum in a city; constant wind sound on a coast.
Sound Signal	Schafer/WSP	Foreground sound listened to consciously, conveying information or warning ⁶	Ambulance siren, phone ringing, spoken announcement.
Soundmark	Schafer/WSP	Unique, culturally significant sound identifying a specific place ⁶	Big Ben chimes in London; specific factory whistle in an industrial town.
Sound Event	General/Schafer	An individual, identifiable sonic occurrence with a beginning and end ⁴²	A passing car, a bird singing its song, a brief conversation.
Pleasantness	ISO 12913 / Affect Models	Perceived hedonic quality (valence) of the soundscape (e.g., pleasant, annoying, calm) ³⁰	Rating a park soundscape as relaxing due to birdsong and water sounds.
Eventfulness	ISO 12913 / Affect Models	Perceived level of activity/stimulation (arousal) in the soundscape (e.g., eventful, uneventful, vibrant, monotonous) ³⁰	Rating a busy market square as lively and eventful, or a quiet library as uneventful.
Acoustic Comfort	General/Soundscape	A state of satisfaction with the acoustic environment, often implying pleasantness and lack of annoyance ³⁰	Feeling comfortable and undisturbed by sounds while working in an office or relaxing at home.
Appropriateness / Congruence	Soundscape Research	Perceived suitability or consistency of the soundscape with the context (place, activity, visual) ⁵²	Feeling that the sound of waves is appropriate at the beach, but inappropriate in an office.

This table provides a simplified overview; definitions and applications can be more nuanced.

III. Objective Methodologies for Soundscape Assessment and Analysis

While soundscape is defined by perception, understanding the physical characteristics of the acoustic environment is crucial.¹ Objective methodologies aim to quantify these physical aspects, providing the input data for perceptual processes and serving as potential predictors, or indicators, for subjective soundscape evaluations, or descriptors.¹³ The goal is often to develop models that can forecast how people might perceive an acoustic environment based on its measurable properties, thereby aiding design and planning without requiring extensive subjective surveys for every scenario.¹³

A. Traditional Acoustic Parameters (Energy-Based)

These parameters, rooted in traditional acoustics and noise control, primarily measure the energy content of sound.

Sound Pressure Level (SPL): The fundamental measure of sound amplitude, typically expressed in decibels (dB) relative to a reference pressure (20 µPa, the approximate threshold of human hearing).⁵⁹ Because the range of audible pressures is vast, a logarithmic dB scale is used.⁵⁹
Equivalent Continuous Sound Level (Leq): This is the most common metric for environmental noise assessment. It represents the constant sound level that would contain the same total sound energy as the actual fluctuating sound level over a specified time period (T).¹⁴ It is essentially a time-averaged root-mean-square (RMS) sound pressure level.⁶¹ The calculation involves integrating the squared sound pressure over time T and normalizing it.⁶²

A-weighting (LAeq): To better reflect human hearing sensitivity, which varies with frequency, the A-weighting filter is commonly applied, resulting in LAeq, measured in dB(A).⁶⁰ This filter de-emphasizes low and very high frequencies.
Applications: LAeq is used extensively in noise regulations and standards (e.g., ISO 1996 ⁶⁴) for various time periods, such as LAeq,16h (daytime) or LAeq,8h (work exposure or nighttime).¹⁴
Limitations for Soundscape: A major drawback of Leq is that it averages out temporal fluctuations and ignores spectral content.¹⁴ Two sound environments with identical LAeq values can sound vastly different and elicit completely different perceptual responses (e.g., steady traffic noise vs. intermittent birdsong).²⁵ Its correlation with subjective annoyance or pleasantness is often weak, especially at moderate or low levels or for sounds with distinct temporal or tonal characteristics.¹⁴
Day-Evening-Night Level (Lden) and Day-Night Level (Ldn): These are 24-hour Leq-based indicators designed to account for increased human sensitivity to noise during evening and nighttime periods.¹⁴

Lden: Calculates the A-weighted Leq over a full day, but adds a 5 dB penalty to levels during the evening (typically 19:00-23:00) and a 10 dB penalty to levels during the night (typically 23:00-07:00).⁶⁰ It is mandated by the EU Environmental Noise Directive (END) for strategic noise mapping.⁶⁸
Ldn: Similar to Lden, but typically applies only the 10 dB nighttime penalty.⁶⁰ It is commonly used in the United States.⁶⁸
Limitations for Soundscape: While accounting for time-of-day sensitivity, Lden and Ldn still suffer from the fundamental limitations of Leq, being energy averages that do not capture perceptual nuances or sound source characteristics.¹⁴
Percentile Levels (Ln): These statistical metrics describe the noise level exceeded for n% of the measurement time.⁶⁰

Common examples include L10 (level exceeded 10% of the time, often related to louder, intermittent events), L50 (median level), and L90 (level exceeded 90% of the time, often representing background noise).⁶⁰
Limitations for Soundscape: They provide information about the statistical distribution and variability of noise levels but still lack direct perceptual relevance regarding sound quality.

The inadequacy of these energy-based metrics to fully capture the human experience of sound environments was a primary driver for the development of the soundscape approach. While necessary for regulatory compliance and characterizing overall noise exposure, they are insufficient for understanding or predicting perceived soundscape quality.

B. Psychoacoustic Parameters (Perception-Based)

Psychoacoustics bridges the gap between physical sound and subjective perception by defining parameters that quantify specific auditory sensations.¹³ These metrics aim to correlate better with human experience than simple energy levels by incorporating models of auditory processing, such as frequency masking, critical bands, and temporal integration.¹⁵

Loudness (sone): Quantifies the perceived intensity or “volume” of a sound.²² Unlike SPL, loudness accounts for the ear’s varying sensitivity across frequencies (as described by equal-loudness contours) and the phenomenon of masking (where one sound makes another harder to hear).²² Calculation methods (e.g., Zwicker/ISO 532-1 ²², Moore/Glasberg) typically involve analyzing the sound spectrum in critical bands (approximating the frequency resolution of the ear) and applying masking models.²² The unit “sone” is designed to be linear with perception, meaning 2 sone sounds twice as loud as 1 sone.⁷¹ Time-varying loudness models capture fluctuations over time.⁷¹ Loudness generally shows a better correlation with perceived volume than SPL.²³
Sharpness (acum): Measures the sensation of “brightness” or “piercingness” associated with high-frequency content in a sound.²² Calculated based on the distribution of specific loudness across critical bands, with higher frequencies given more weight (e.g., DIN 45692 method).²² High sharpness can contribute to annoyance.¹⁵
Roughness (asper): Quantifies the perceived “rasping” or “buzzing” quality caused by rapid (typically 15-300 Hz) amplitude or frequency modulations in a sound.²³ Relevant for evaluating certain mechanical noises or vocalizations.
Fluctuation Strength (vacil): Measures the perception of slower (< 20 Hz) amplitude or frequency modulations, corresponding to a “fluctuating” or “wavering” sensation.²³
Tonality: Indicates the presence and prominence of distinct tones within a sound.⁵⁸ Tonal components are often associated with increased annoyance, even at low overall levels.¹⁵
Impulsivity: Relates to the occurrence of brief, high-energy sound events (e.g., impacts, clicks) ¹⁴, which can also increase annoyance.

These psychoacoustic parameters provide a more nuanced description of the acoustic environment, capturing features relevant to perception that Leq obscures.¹⁵ They can help explain why sounds with similar energy levels are perceived differently and may correlate better with subjective ratings of pleasantness, eventfulness, or annoyance.⁵⁸ They form the basis for “psychoacoustic mapping,” which aims to visualize the spatial distribution of perceived sound qualities beyond just noise levels.¹⁵

C. Spectral Analysis Techniques

Analyzing the frequency content of sound is fundamental to both traditional and psychoacoustic assessment.

Frequency Analysis: Understanding how sound energy is distributed across different frequencies is crucial, as human hearing and perception are highly frequency-dependent.¹⁴
Octave and 1/3 Octave Band Analysis: These are standard methods that divide the audible frequency spectrum into contiguous bands (with bandwidths of one octave or one-third of an octave) and measure the sound level within each band.¹⁵ This provides a spectral profile of the sound and is often the first step in calculating psychoacoustic parameters like loudness.²²
Spectrograms: These are powerful visualization tools that display the intensity of sound across frequency (y-axis) over time (x-axis), typically using color or grayscale to represent intensity.⁷⁵ Spectrograms allow for the visual identification of sound events, their duration, frequency characteristics (e.g., tones, broadband noise), and temporal patterns. They are widely used in bioacoustics and are increasingly used as input features for machine learning models in soundscape analysis.⁷⁵

D. Sound Source Identification and Separation

Recognizing that the source of a sound heavily influences its perception (e.g., birdsong vs. traffic noise), identifying and quantifying the contribution of different sound sources is a critical aspect of objective soundscape analysis.⁵²

Manual Identification: Human listeners can annotate recordings, identifying sound events and their sources. This is often used to create “ground truth” data for training automated systems but is time-consuming for large datasets.
Acoustic Indices (Ecoacoustics): Fields like ecoacoustics have developed various indices (e.g., Acoustic Complexity Index (ACI), Normalized Difference Soundscape Index (NDSI), Bioacoustic Index (BI)) calculated from recordings to quantify characteristics of the soundscape, often related to biodiversity or the balance of biophony (biological sounds) vs. anthrophony (human-caused sounds).⁶⁹ While primarily designed for ecological monitoring, these indices are sometimes explored for their correlation with human perception in urban settings ⁶⁷, though their effectiveness in complex urban environments is still under investigation.⁸²
Machine Learning (ML) / Artificial Intelligence (AI) Approaches: The proliferation of acoustic data from long-term monitoring and citizen science has spurred the development of automated methods using ML/AI.²

Acoustic Event Detection (AED) / Sound Event Detection (SED): This task involves automatically identifying what sounds are present in a recording and when they occur.⁷⁶ Deep learning models, particularly Convolutional Neural Networks (CNNs), Recurrent Neural Networks (RNNs), and combinations like CRNNs, are state-of-the-art.⁷⁵ These models are typically trained on labeled data, often using spectrograms or related features (e.g., Mel-Frequency Cepstral Coefficients – MFCCs, Mel-band energies) as input.⁷⁵ A challenge is dealing with “weakly labeled” data, where only the presence/absence of a sound in a longer clip is known, not its exact timing; techniques like Multiple Instance Learning (MIL) are used to address this.⁸⁴
Source Separation: This aims to computationally “unmix” an audio recording containing multiple overlapping sounds into its constituent source signals (e.g., separating speech from background music).⁷⁵ Traditional methods include Independent Component Analysis (ICA) and Non-negative Matrix Factorization (NMF).⁷⁶ Deep learning techniques, such as autoencoders, U-Nets (a type of CNN), and Generative Adversarial Networks (GANs), are increasingly employed, often operating on spectrograms.⁷⁵ Source separation allows for the analysis of individual components within complex soundscapes.⁷⁶
Combined Approaches: Research is also exploring AI models that can jointly perform sound recognition and perceptual appraisal, for example, predicting pleasantness and eventfulness scores directly from audio recordings.⁸³

The clear trend in objective methodologies is a move beyond simplistic energy averaging towards incorporating perceptual models (psychoacoustics) and leveraging computational power (AI/ML) to extract richer information about the temporal structure, spectral content, and contributing sources within the acoustic environment. This shift is driven by the need for objective indicators that correlate more meaningfully with the subjective experience of the soundscape. While traditional metrics like Leq and Lden remain essential for regulatory purposes due to their standardization and simplicity, they are insufficient for capturing the nuances relevant to soundscape quality. Psychoacoustic parameters offer a step closer to perception, while AI-based source identification and analysis provide powerful tools for dissecting complex urban sound environments. PhD students entering the field must therefore develop an understanding of the strengths and limitations of each approach and stay abreast of the rapid advancements in computational soundscape analysis. The choice of metrics should always be guided by the specific research question, whether it pertains to noise impact assessment, perceptual modeling, or intervention design.

IV. Subjective Methodologies for Soundscape Evaluation

Given that soundscape is fundamentally defined by human perception and experience in context ¹, subjective methodologies are indispensable for its evaluation. These methods directly engage with listeners to capture their feelings, judgments, and understanding of acoustic environments.² Subjective data provides the essential “ground truth” regarding soundscape quality, serving as the benchmark against which objective indicators are validated and predictive models are built.¹³

A. In-situ Data Collection Methods (Field Studies)

These methods involve assessing soundscapes in their actual physical and social context, maximizing ecological validity.

Soundwalks: A cornerstone technique in soundscape research, the soundwalk involves participants walking through an area with a deliberate focus on listening to the acoustic environment.¹⁰ Typically, a moderator guides participants along a pre-defined route with specific stopping points.³⁴ At these points, participants engage in a focused listening period (e.g., 3 minutes) before recording their perceptions, usually via questionnaires.³⁴ Soundwalks aim to capture context-sensitive data, acknowledging that perception is shaped by the real-world setting.⁸⁵
ISO 12913-2 Protocols: The standard outlines several approaches ²⁷:

Method A: Employs questionnaires administered at listening points during the soundwalk, typically using 5-point Likert scales to rate Perceived Affective Quality (PAQ) attributes (Pleasant, Annoying, etc.) and sound source dominance.³⁴
Method B: Similar to Method A but utilizes continuous category scales (e.g., sliders) with verbal anchors like ‘not at all’ to ‘extremely’.²⁷
Method C (Narrative Interview): While listed under data collection methods in the standard, this is typically a seated interview focused on broader experiences with sound, rather than an active walk (discussed further below).²⁷

Influencing Factors: The specific path chosen for a soundwalk can influence overall assessment; for example, experiencing a transition from a noisy to a quiet area may result in higher ratings of acoustic comfort compared to the reverse sequence.⁹⁰
Advantages: High ecological validity, captures the richness of real-world context including multisensory inputs and social dynamics.
Disadvantages: Lack of experimental control over environmental variables (weather, transient events), logistical complexity, time-consuming nature, potential difficulty in recruiting large samples, challenges in exact replication.⁸⁵
Questionnaires / Surveys (In-situ): Questionnaires are the most common tool for gathering subjective soundscape data, often administered during soundwalks but also used independently at specific locations.⁴
Typical Content: Soundscape questionnaires generally cover several domains ³⁴:

Sound Source Identification/Dominance: Asking participants to identify audible sounds and rate their perceived prominence (e.g., traffic, human voices, birdsong, water sounds).³⁴
Perceived Affective Quality (PAQ): Assessing emotional responses using standardized attributes like the ISO 8 (Pleasant, Annoying, Eventful, Uneventful, Vibrant, Monotonous, Calm, Chaotic).³⁰
Overall Evaluation: Questions about overall satisfaction, quality, appropriateness, or preference for the soundscape.³⁴
Acoustic Comfort: Direct assessment of comfort levels.⁴
Contextual Information: Data on the participant (demographics, noise sensitivity, expectations, activity) and the environment (visual aspects, weather).⁵²
Scaling Methods:

Likert Scales: Widely used, especially in ISO Method A, asking for degree of agreement (e.g., 1=Strongly Disagree to 5=Strongly Agree) with attribute statements.³⁴ However, studies have identified potential issues like scaling bias (ratings for opposite poles like ‘Pleasant’ and ‘Annoying’ are not perfectly mirrored), task distinction (rating ‘Pleasant’ might prime focus on positive sounds, while rating ‘Annoying’ primes focus on negative ones), and limited scale resolution potentially masking nuances.⁴⁹
Semantic Differential Scales: Present bipolar adjective pairs (e.g., Noisy — Calm; Artificial — Natural) along a scale (often 5 or 7 points), asking participants to rate where the soundscape falls.⁴ These are frequently used for assessing PAQ or acoustic comfort.³⁰
Self-Assessment Manikins (SAM): Non-verbal, pictographic scales used to rate emotional dimensions like valence (pleasure), arousal (excitement), and dominance (control).⁸⁶
Narrative Interviews (ISO Method C): This qualitative method involves in-depth, guided conversations exploring participants’ broader relationship with and experiences of sound, often in their living environment.²⁷ It focuses on themes like satisfaction with the sonic environment, daily routines related to sound, effects of different sounds, and personal coping strategies.²⁷ While providing rich, detailed insights, it yields less standardized data compared to questionnaires and typically involves smaller sample sizes.

B. Laboratory-Based Data Collection Methods

These methods sacrifice some ecological validity for increased experimental control, repeatability, and efficiency.

Listening Tests: Participants evaluate pre-recorded sound stimuli under controlled conditions.³⁷

Stimuli Reproduction: High-fidelity reproduction is crucial. Binaural recording techniques (using microphones placed in ear canals or on a Head-and-Torso Simulator – HATS) aim to capture the sound field as a human listener would experience it, preserving spatial cues.⁵ Ambisonics is another technique used to capture and reproduce the full spherical sound field, often played back over loudspeaker arrays or binaurally rendered for headphones.⁹⁵ Accurate calibration of playback levels is essential.⁹⁷
Environment: Tests are conducted in acoustically controlled spaces like quiet rooms, semi-anechoic chambers, or specialized listening rooms to minimize external interference.³⁷
Procedure: Participants listen to stimuli (often short excerpts) via headphones or loudspeakers and provide ratings using questionnaires, typically similar to those used in field studies.³⁷ Group testing is possible, allowing for efficient data collection.³⁷
Advantages: High degree of control over stimuli and environment, excellent repeatability, ability to systematically manipulate specific acoustic variables, efficiency in data collection.³⁷
Disadvantages: Reduced ecological validity due to the absence of real-world context (visual, olfactory, thermal, social cues), potential artificiality of the listening situation (e.g., headphone listening), reliance on memory for contextual judgments if stimuli are decontextualized.⁷⁷
Virtual Reality (VR) / Augmented Reality (AR) Methods: These immersive technologies attempt to bridge the gap between laboratory control and field realism.⁹⁷

Technology: VR typically involves Head-Mounted Displays (HMDs) presenting 360-degree video or computer-generated visual scenes, coupled with spatial audio (binaural or Ambisonic rendering via headphones) that responds to head movements.⁵ AR overlays virtual elements onto the real world.
Applications: VR allows researchers to conduct “virtual soundwalks” ⁸⁶, evaluate existing environments remotely, or, crucially, assess the perceptual impact of proposed designs or interventions before they are built.⁵
Ecological Validity: A key focus is ensuring the VR experience sufficiently replicates the real-world perception. Studies comparing VR assessments to in-situ soundwalks suggest that VR can be a valid tool, provided the audiovisual stimuli are carefully recorded, calibrated, and rendered to achieve a high sense of immersion and realism.⁵ However, results should still be interpreted with caution, as laboratory settings might amplify certain effects.⁹⁷
Advantages: Offers greater control than field studies while providing higher contextual immersion than traditional lab tests; enables evaluation of hypothetical scenarios; can be more engaging for participants.⁹⁵
Disadvantages: Requires specialized equipment and technical expertise; potential for cybersickness; challenges in achieving perfect audiovisual fidelity and congruence; ensuring adequate representation of all relevant contextual factors.⁵

C. Insights and Implications from Subjective Methodologies

The choice between field and laboratory methods involves navigating a fundamental trade-off between ecological validity and experimental control. In-situ methods like soundwalks maximize realism by capturing the full context in which soundscapes are experienced, but they are susceptible to uncontrolled variables and are logistically demanding.⁸⁵ Laboratory listening tests offer precise control over stimuli and the environment, facilitating repeatability and causal inference, but they strip away the rich context that significantly shapes real-world perception.³⁷ VR/AR technologies represent a promising attempt to reconcile this tension, offering controlled immersion ⁹⁷, although their validation is an ongoing process requiring meticulous attention to technical details like audio rendering and reflection modeling.⁵ Researchers must carefully weigh these factors and select the methodology best suited to their research question, acknowledging the inherent strengths and limitations of their chosen approach.

While standardization efforts, particularly ISO 12913-2, provide valuable frameworks for data collection ⁸⁸, their practical application reveals ongoing challenges. The recommended Likert scales for PAQ assessment (Method A) have demonstrated potential biases and limitations in resolution.⁴⁹ Translating the standardized English attributes into other languages and cultural contexts requires careful validation to ensure conceptual equivalence, as meanings can shift significantly.²⁸ Furthermore, the standard attribute set may not be optimally suited for all environments; for example, attributes relevant to urban squares might differ from those most salient in quiet natural areas or indoor offices.⁹⁹ This suggests that while the ISO standards offer a crucial starting point for comparability, researchers may need to adapt or supplement them depending on the specific context and population, and full compliance with the standards remains relatively uncommon in published studies.³⁵

Finally, the specific design of any subjective assessment method—be it the wording and scaling of questionnaire items, the sequence of locations in a soundwalk, or the fidelity and duration of stimuli in a VR simulation—can significantly impact the results obtained.⁵ This underscores the need for meticulous methodological planning, piloting, and transparent reporting in soundscape research. New PhD students should critically evaluate the methods used in existing literature and carefully justify their own methodological choices, considering the trade-offs and potential influences on their findings.

Table IV.1: Comparison of Subjective Soundscape Assessment Methods

Method	Key Characteristics	Typical Application	Strengths	Limitations	Ecological Validity	Experimental Control
Soundwalk (e.g., ISO Method A/B)	In-situ guided walk; focused listening at stops; questionnaire/scale ratings ²⁷	Assessing existing environments; participatory planning; comparing locations ³⁴	High ecological validity; captures real context (multisensory, social) ⁸⁵	Low control; weather/event dependency; time-consuming; potential small sample size; replication difficult ⁸⁵	High	Low
In-situ Questionnaire/Survey	Administered at a specific location; assesses perception, sources, PAQ, context ⁴	Point-based assessment; often combined with soundwalks or objective measures ³⁴	Captures context; relatively simple to administer	Static (no movement); relies on participant attention at that moment; potential sampling bias	High	Low
Narrative Interview (ISO Method C)	In-depth qualitative interview; explores broader experiences/relationships with sound ²⁷	Understanding long-term perspectives; exploring personal meaning; qualitative research ²⁷	Rich qualitative data; deep understanding of individual context	Not standardized; small sample size; relies on memory; time-intensive analysis	Moderate	Low
Laboratory Listening Test (Binaural/Ambisonic)	Controlled playback of recorded stimuli (headphones/speakers); questionnaire ratings ³⁷	Comparing stimuli under controlled conditions; isolating variables; testing specific sounds ³⁷	High control; high repeatability; efficiency (group testing); isolates auditory modality ³⁷	Low ecological validity (lack of context); artificial listening situation; potential fatigue ⁷⁷	Low	High
Virtual Reality (VR) Simulation	Immersive audiovisual reproduction (HMD + spatial audio); interactive or passive viewing ⁵	Assessing existing/hypothetical environments; virtual soundwalks; testing interventions ⁹⁵	Combines control with immersion; tests non-existent scenarios; potentially engaging ⁹⁵	Technical complexity/cost; cybersickness risk; validation needed; ensuring fidelity/congruence ⁵	Moderate-High	Moderate-High

V. Urban Soundscapes, Human Health, and Well-being

The acoustic environment of cities has profound and well-documented effects on the physical and mental health of their inhabitants. Traditionally, research focused almost exclusively on the detrimental impacts of noise pollution – unwanted or disturbing sound.⁷⁰ However, the soundscape perspective introduces a crucial duality: while noise undeniably harms health, positive and desired soundscapes can actively promote well-being, restoration, and overall quality of life.¹⁰² Understanding this dual nature is essential for moving beyond simple noise mitigation towards the creation of truly health-supportive urban environments.¹⁶

A. Negative Impacts: Noise Pollution and Health

Environmental noise, particularly from transportation (road, rail, air traffic), is recognized as a major public health issue, second only to air pollution in terms of environmental burden of disease in Europe.¹⁰² The World Health Organization (WHO) and the European Environment Agency (EEA) estimate that millions of Europeans are exposed to noise levels considered harmful to health, leading to a significant loss of healthy life years (Disability-Adjusted Life Years, DALYs) annually due to noise-induced health problems.¹⁰²

Cardiovascular Effects: A substantial body of epidemiological evidence links chronic exposure to environmental noise, especially transportation noise assessed using metrics like Lden and Lnight, to an increased risk of major cardiovascular diseases.¹⁰⁵ Studies consistently report associations with:

Hypertension (High Blood Pressure): Noise acts as a stressor, triggering the release of catecholamines and cortisol, which acutely increase blood pressure and heart rate.¹⁰⁷ Chronic exposure, particularly at night, can disrupt the normal nocturnal dip in blood pressure and contribute to the development of sustained hypertension.¹⁰⁷ Meta-analyses suggest increased risk associated with road traffic and occupational noise, with some evidence for aircraft noise, though findings can vary based on study design and population characteristics.¹⁰⁸
Ischemic Heart Disease (IHD) / Myocardial Infarction (Heart Attack): The stress response to noise can also lead to endothelial dysfunction (impaired blood vessel function), increased oxidative stress, inflammation, and changes in blood lipids and coagulation, all of which contribute to atherosclerosis and increase the risk of heart attacks.¹⁰⁵ WHO estimates attribute tens of thousands of new IHD cases and premature deaths annually in Europe to noise exposure.¹⁰⁶
Stroke: Similar mechanisms involving stress, hypertension, and vascular damage link noise exposure to an increased risk of stroke.¹⁰⁹ The WHO has established guideline values (e.g., Lden < 53 dB for road traffic, Lnight < 40-45 dB) aimed at preventing these adverse cardiovascular outcomes.¹⁰⁸

Sleep Disturbance: Noise is a primary cause of sleep disruption.¹⁰⁵ Even at levels that do not cause full awakening, noise events during sleep can trigger physiological arousal responses (increased heart rate, blood pressure, stress hormone release) and alter sleep architecture (reducing deep restorative sleep and REM sleep, increasing lighter sleep stages).¹⁰⁵ Chronic sleep disturbance contributes significantly to the burden of disease (estimated at over 900,000 DALYs annually in Western Europe ¹⁰⁷) and has knock-on effects on daytime functioning, including fatigue, reduced performance, and increased risk of accidents.¹⁰⁵ Nocturnal noise exposure is considered particularly detrimental to cardiovascular health due to these sleep disruptions and associated physiological stress.¹⁰⁷
Stress and Mental Health: Noise acts as a potent environmental stressor.¹⁰⁷ Chronic exposure can lead to heightened physiological stress responses.¹⁴ Psychologically, noise is strongly linked to annoyance, a significant negative feeling encompassing disturbance, irritation, and dissatisfaction, which itself impacts quality of life.¹⁴ Studies also suggest associations between noise exposure and increased risk of anxiety, depression, and general mental distress.¹⁴
Cognitive Impairment: Noise exposure, particularly in learning environments, has been shown to negatively impact cognitive functions, especially in children.¹⁰⁵ Effects include impaired reading ability, attention deficits, and reduced memory performance.¹⁴ The WHO quantifies the burden from noise-induced cognitive impairment in children as significant.¹⁰⁷

B. Positive Impacts: Restorative and Salutogenic Soundscapes

Contrasting with the harmful effects of noise, research increasingly demonstrates the potential for positive soundscapes to actively enhance health and well-being.¹⁰³ This aligns with salutogenic approaches in public health, focusing on factors that support health rather than just those that cause disease.

Restoration Potential: A key benefit of positive soundscapes, particularly those rich in natural sounds, is their capacity to facilitate psychological restoration – recovery from mental fatigue and stress.⁷⁴ Two main theories explain this:

Attention Restoration Theory (ART): Posits that natural environments engage “soft fascination” (effortless attention) and provide a sense of “being away,” “extent,” and “compatibility,” allowing directed attention resources to replenish.¹⁶ Natural sounds contribute significantly to these qualities.¹¹⁶
Stress Recovery Theory (SRT): Suggests that exposure to non-threatening natural environments reduces physiological arousal (stress) through innate responses shaped by evolution.¹⁰³ Empirical studies consistently support these theories in the auditory domain. Field experiments show that spending time in natural environments with natural sounds improves attention levels compared to environments with traffic or machine noise.¹¹⁶ Laboratory studies and meta-analyses confirm that listening to natural sounds (compared to silence or urban noise) leads to significant improvements in mood, cognitive performance (e.g., attention), and reductions in physiological stress indicators (heart rate, blood pressure, skin conductance) and self-reported stress and annoyance.⁴⁸ Specific natural sounds show particular strengths: water sounds are strongly linked to improved positive affect and health outcomes, while bird sounds appear particularly effective at reducing stress and annoyance.⁴⁸ Soundscape attributes like pleasantness, calmness, and perceived naturalness are identified as key mediators of these restorative effects.⁷⁴

Overall Well-being and Quality of Life: Beyond specific restorative effects, positive soundscapes contribute broadly to perceived quality of life, satisfaction with the living environment, and general well-being.¹⁶ Access to quiet areas and environments judged as having high soundscape quality is associated with higher vitality and greater satisfaction.¹¹⁵ The concept of acoustic comfort, aiming for pleasant and non-disturbing environments, is central to this aspect.⁴ Interventions that improve soundscape quality, such as urban regeneration projects incorporating pleasant sounds, have been shown to reduce negative emotions and perceived stress while increasing positive feelings among users.¹⁶
Perceived Safety: The soundscape also influences feelings of security in urban spaces.¹²¹ Certain sounds, particularly non-threatening human sounds (like conversation or footsteps), can increase perceived safety by creating a sense of social presence – the feeling that others are nearby, potentially offering help or deterring crime.¹²¹ Natural sounds like water or birdsong have also been linked to increased perceived safety in some contexts, possibly by enhancing pleasantness or masking potentially threatening sounds.¹²¹ Conversely, silence or ambiguous, sudden noises can decrease perceived safety. This highlights how soundscape design can potentially influence fear of crime and the usability of public spaces, particularly at night.¹²¹

C. Insights and Implications regarding Health and Well-being

The evidence clearly demonstrates that urban sound has a bidirectional impact on health: noise pollution is a significant environmental health risk, causing stress, sleep disturbance, and contributing to cardiovascular disease, while positive soundscapes, especially those featuring natural sounds, offer restorative benefits, improve mood, enhance cognitive function, and contribute to overall well-being.⁴⁸ This duality fundamentally reframes soundscape management. It is not merely about mitigating a negative (noise) but also about actively cultivating a positive (health-supportive soundscapes).¹⁶ This perspective elevates soundscape design from a niche acoustic concern to a potential public health strategy.¹⁰²

The mechanisms linking sound to health outcomes are multifaceted, involving both direct physiological pathways and indirect psychological ones. Noise triggers physiological stress responses via the autonomic nervous system and endocrine system, leading to downstream effects like endothelial dysfunction and inflammation.¹⁰⁷ Soundscape perception, however, is mediated by cognitive and affective processes. Attributes like pleasantness, eventfulness, and perceived naturalness influence emotional states and cognitive restoration, as explained by theories like ART and SRT.⁷⁴ Perceived safety is linked to the interpretation of social cues embedded in the soundscape.¹²¹ This complexity implies that effective interventions must consider both the physical characteristics of sound and how those sounds are perceived and interpreted within a specific context.

The consistent finding that natural sounds offer significant health and well-being benefits provides a strong evidence base for specific design strategies.⁴⁸ Integrating natural elements like water features ¹²² and vegetation that supports audible wildlife (e.g., birds ⁸²) into urban design is not just an aesthetic choice but a potential health intervention. Preserving existing natural soundscapes, even within busy urban parks, is crucial for providing accessible restorative experiences.⁴⁸ PhD research has a vital role to play in further clarifying these health links, quantifying the benefits of specific soundscape interventions in diverse populations and contexts, and developing frameworks for integrating soundscape considerations into public health policy and health-promoting urban design.

VI. Perception and Appraisal: Understanding the Listener’s Experience

The core principle of the soundscape concept is its focus on perception: the soundscape exists not in the physical waves themselves, but in how those waves are “perceived or experienced and/or understood by a person or people, in context”.¹ This means the listener is not a passive microphone simply registering sound levels, but an active interpreter who constructs meaning and evaluates the acoustic environment based on a complex interplay of auditory input, context, and individual factors.² Soundscape appraisal is the process through which this evaluation occurs.¹⁰ Understanding the factors that shape this perception and appraisal is therefore central to the field.

A. Individual Differences

People respond differently to the same acoustic environment due to a variety of personal characteristics.

Noise Sensitivity: This is perhaps the most studied individual factor. Defined as an internal physiological and psychological state that increases reactivity to noise ¹²⁴, noise sensitivity is a stable trait varying across the population, with estimates suggesting 12-40% of people may be noise sensitive.¹²⁴ Highly noise-sensitive individuals report greater annoyance from noise, are more prone to noise-induced sleep disturbance, and may experience more negative psychological symptoms like anxiety and depression.¹²⁴ Consequently, noise sensitivity significantly influences soundscape appraisal, often leading to lower tolerance for urban sounds and a stronger preference for quiet or natural environments.⁵² It has been linked to personality traits, particularly higher neuroticism and introversion.¹²⁴
Personality Traits: Beyond noise sensitivity, broader personality dimensions, such as those in the Big Five model (Neuroticism, Extraversion, Openness, Agreeableness, Conscientiousness), can influence how individuals react to their sonic environment.¹²⁴ For example, introverts may find complex or loud soundscapes more draining than extraverts. However, research in this area is still developing, and interactions with factors like age and gender need careful consideration.¹²⁴
Demographic Factors: Age, gender, education level, occupation, socioeconomic status, and residential history (e.g., urban vs. rural background, duration of residence) have all been found to correlate with soundscape perception and preferences in various studies.⁵⁵ For instance, some studies suggest females may report higher noise sensitivity or lower tolerance for certain sounds ⁵⁵, while older individuals or those more familiar with a place might show greater tolerance for its typical sounds.⁹² Higher education or socioeconomic status has sometimes been linked to lower tolerance for noise.⁹² However, findings across studies are not always consistent, suggesting complex interactions and the importance of context.⁵⁵ Long-term sound experience, such as the acoustic environment at home, can significantly affect sound level evaluations in other spaces.⁹²
Expectations: What people expect to hear in a particular place strongly shapes their perception and evaluation.³⁶ Expectations are built from prior experience, knowledge of the place function, and cultural norms.⁹³ A sound might be perfectly acceptable if expected (e.g., traffic on a busy street) but highly annoying if unexpected (e.g., loud music in a library). Importantly, expecting a sound is different from finding it pleasant; one might expect traffic noise but still find it unpleasant.⁹³ Expectations also extend to the types of activities suitable for a place and the perceived behaviour of others.⁹³ This aligns with Barry Truax’s concept of “soundscape competence,” the listener’s ability to interpret sounds based on learned associations and experience.⁹³
Attitudes and Motivations: A person’s attitude towards the sound source (e.g., finding construction noise necessary vs. unnecessary) or the producer of the sound influences appraisal.⁴⁷ Likewise, the motivation for being in a space affects perception; someone seeking quiet relaxation in a park will evaluate sounds differently than someone passing through or engaging in active recreation.¹²⁵
Psychological State: Temporary states like mood, stress level, or fatigue can alter how sounds are perceived and evaluated.⁷⁴
Aural Diversity / Hearing Ability: Variations in hearing ability, including hearing loss or conditions like tinnitus, will naturally affect sound perception and should be considered, though this aspect is sometimes overlooked in soundscape studies.⁸⁶

B. Cultural Variations

Just as individuals differ, cultural backgrounds and geographical contexts shape collective experiences and interpretations of soundscapes.⁴⁵ Language influences how sounds are described and categorized ²⁸, and cultural norms affect expectations and values associated with different sounds and places.⁴⁷

Evidence from Cross-Cultural Studies: Comparative research has revealed significant cultural differences in soundscape evaluation:

Dimensional Importance: Studies comparing European and Chinese participants found that while both groups used Pleasantness and Eventfulness dimensions, Chinese participants tended to give more weight to Eventfulness, while European participants (specifically Croatian in one study) emphasized Pleasantness.⁴⁷ Similar differences in the structure of Eventfulness were found between French, Korean, and Swedish participants.¹²⁸
Sound Source Perception: The relationship between sound sources and perceived quality varies. The positive link between natural sounds and pleasantness/calmness was found to be stronger for European participants than for Chinese participants.⁴⁷ Europeans associated vibrant soundscapes more with human sounds, whereas Chinese participants linked vibrancy more with natural sounds.⁴⁷ Preferences for specific sounds like insect sounds or church bells also differ culturally.⁴⁷
Attribute Interpretation: The meaning and evaluation of specific PAQ attributes can differ. Studies translating the ISO attributes have found variations in how terms like ‘monotonous’, ‘exciting’, ‘chaotic’, or ‘eventful’ are interpreted and rated across languages like French, Korean, Swedish, English, Arabic, Japanese, and Vietnamese.⁵¹
Challenges: Comparing findings across cultures is complicated by the lack of standardized protocols and validated translations of assessment tools.⁴⁷ Projects like the Soundscape Attributes Translation Project (SATP) are working to develop and validate translations of the ISO attributes in multiple languages to facilitate reliable cross-cultural research.²⁸

C. Context Dependency

Perception is inseparable from context. The same acoustic signal can be interpreted entirely differently depending on the surrounding circumstances.

Place and Function: The type of environment (park, plaza, street, residential area, office, hospital) and its intended function heavily influence soundscape expectations and evaluations.⁵² A study in a historical block clearly showed that residential, commercial, and cultural/leisure zones had distinct dominant sound sources (e.g., more mechanical noise in residential/commercial, more natural sounds in cultural/leisure) and that these sounds had different impacts on perceived pleasantness and visual satisfaction depending on the zone’s function.⁵³
Activity: The activity a person is engaged in (or intends to engage in) is a critical contextual factor.⁹¹ Sounds appropriate for socializing might be disruptive for reading or resting. People engaged in solitary activities often evaluate soundscapes differently (e.g., less favorably) than those engaged in social interaction.⁹¹
Time: Soundscapes naturally vary over time (diurnally, seasonally), and perception can also change depending on the time of day or year.⁵²
Social Context: The presence and behavior of other people contribute to the soundscape and influence its perception.⁹³

D. Audiovisual and Multisensory Interactions

Perception is inherently multisensory. What we see, smell, or even feel profoundly interacts with what we hear, shaping the overall soundscape experience.

Audiovisual Interaction: The link between sound and sight is particularly strong and well-studied in soundscape research.⁵⁴

Visual Influence on Auditory Perception: Visual elements significantly modulate soundscape appraisal.⁵⁴ Views of nature (greenery, water) can reduce noise annoyance and increase perceived pleasantness, even mitigating the negative perception of traffic noise.⁵⁴ The visual appearance of the built environment (e.g., building density, street proportions) also plays a role.⁵⁴ Even the visibility of a sound source can alter annoyance levels, although the direction of this effect can vary.¹²⁶
Audiovisual Congruence: Consistency or harmony between what is seen and heard is crucial for positive environmental perception.¹⁶ A congruent audiovisual experience, where sounds match the visual scene and expectations (e.g., water sounds near a visible fountain), enhances satisfaction, perceived quality, and restorativeness.⁴ Incongruence can lead to confusion or reduced pleasantness.
Individual Differences: People vary in how they integrate audiovisual information, potentially related to factors like attention and working memory capacity.¹²⁶
Broader Multisensory Approaches: Recognizing that experience extends beyond sight and sound, emerging research explores interactions involving other senses like olfaction (smell) and touch.² Studies in urban micro-green spaces, for instance, show that combinations of visual, auditory (natural sounds), and olfactory (plant scents) stimuli can be more effective for attention restoration and can optimize spatial perception compared to single-sensory inputs.¹³⁵ Specific sounds and smells can even guide visual attention towards corresponding environmental features.¹³⁵ This points towards the potential of designing holistic, multisensory experiences in urban spaces.

E. Insights and Implications regarding Perception and Appraisal

The extensive research on soundscape perception yields several critical understandings for emerging researchers. Firstly, it is undeniable that soundscape perception is a complex construction, far removed from a simple registration of physical sound.¹ It is profoundly shaped by the listener’s internal world—their psychological traits (noise sensitivity, personality), physiological state, demographic background, past experiences, and current expectations—as well as the multifaceted external context, including the physical setting, social situation, cultural norms, and crucially, information from other senses, especially vision.⁴⁷ This inherent subjectivity and context-dependency means that simplistic, purely acoustic approaches are inadequate for understanding or predicting how a sound environment will actually be experienced.

Secondly, the concept of appropriateness or congruence emerges as a vital element for positive soundscape appraisal.⁵² People evaluate sounds based on whether they “fit” the place, the activity, their expectations, and the visual scene.⁹¹ Achieving this sense of harmony—between sound and place, sound and activity, sound and sight—appears to be a key goal for successful soundscape design aimed at user satisfaction and well-being.¹⁶

Thirdly, while individual and cultural variability is significant, some general patterns persist, such as the broad preference for natural sounds and aversion to traffic noise.⁴⁸ However, the strength, nuance, and interpretation of these patterns are highly context-dependent.⁴⁷ Human sounds, for example, can be perceived positively as indicators of social vibrancy and safety, or negatively as sources of annoyance, depending heavily on the specific context, cultural background, and individual listener.⁴⁷ This implies that while some general principles may apply, effective soundscape assessment and design demand careful attention to the specificities of each situation.

For PhD students, these points have significant implications. Research designs must rigorously account for the multifaceted influences on perception. This involves clearly defining the study context, measuring relevant individual and cultural variables, employing mixed-methods approaches that capture both quantitative patterns and qualitative nuances, and exercising caution when generalizing findings across different populations, settings, or cultures. Investigating the interplay between sound and other senses represents a particularly rich and growing area for future research contributions.

VII. Integrating Soundscape Principles into Urban Planning and Design Practice

The ultimate goal of much soundscape research is to inform and improve the ways cities are planned, designed, and managed. Integrating soundscape principles into urban planning and design holds the potential to create environments that are not only less noisy but also more pleasant, healthy, restorative, and supportive of a higher quality of life.¹⁶ This involves moving beyond traditional noise control, which focuses solely on reducing decibel levels, towards a more holistic approach that considers the perceptual quality of the entire acoustic environment, treating sound as a potential resource to be managed and designed.¹³

A. The Rationale for Integration

The need to integrate soundscape thinking into urban practice stems from several factors:

Improving Health and Well-being: As detailed in Section V, urban soundscapes have direct impacts on cardiovascular health, sleep, stress levels, cognitive function, perceived safety, and overall well-being.⁴⁸ Planning and design decisions that shape the acoustic environment are, therefore, public health decisions.
Enhancing Quality of Life: Pleasant and appropriate soundscapes contribute significantly to the experiential quality of urban spaces, influencing user satisfaction, place attachment, and the overall livability of cities.⁷⁷
Sustainability: Creating sustainable urban environments requires consideration of environmental quality beyond traditional metrics. Soundscape quality is an important aspect of environmental sustainability, affecting both human experience and potentially urban ecosystems.⁴⁸
Human-Centered Design: The soundscape approach, with its focus on human perception and experience in context, aligns with broader trends towards more human-centered urban design and planning.¹⁶

B. Current State: The Research-Practice Gap

Despite the compelling rationale and a rapidly growing body of academic research, the actual implementation of soundscape principles in routine urban planning and design practice remains limited.² A significant gap persists between the knowledge generated by researchers and its application by practitioners (e.g., urban planners, landscape architects, architects, policymakers). Key barriers contributing to this gap include ³⁸:

Dominance of the Noise Control Paradigm: Planning regulations and professional practices are still largely dominated by a focus on noise levels (dB) and mitigation, treating sound primarily as a pollutant to be controlled below certain thresholds.³⁸
Lack of Awareness and Training: Many practitioners lack awareness of soundscape concepts or specific training in acoustic design principles beyond basic noise control.³⁸ Differences in vocabulary and conceptual frameworks between researchers and practitioners hinder communication.³⁸
Scarcity of Practical Tools and Guidance: There is a perceived lack of accessible, practical tools, clear design guidelines, and compelling case studies specifically tailored for practitioners to implement soundscape principles.³⁸ Existing tools may be geared towards acousticians rather than planners or designers.³⁸
Timing of Consideration: Sound and acoustics are often considered only late in the design process, after major decisions about layout and form have been made, limiting the potential for effective integration.³⁸
Integration Challenges: Difficulties exist in incorporating subjective, qualitative perceptual data into planning systems that often prioritize objective, quantifiable metrics.³⁹
Policy and Regulatory Frameworks: Explicit inclusion of soundscape concepts in planning policies and regulations is still rare, although examples are emerging.³⁹
Resource Constraints: Lack of time, budget, and expertise within planning departments or design firms can be a barrier.⁴⁰

C. Soundscape Design Principles and Strategies

Integrating soundscape requires adopting specific principles and employing a range of design strategies:

Core Principles:

Sound as a Resource: View sound not just as waste, but as an element that can positively shape experience.¹³
Perception-Led: Prioritize human perception and experience in context.¹
Congruence: Aim for harmony between the soundscape, visual landscape, place function, and user activities/expectations.¹⁶
Positive Sound Design: Actively design for pleasant and appropriate sounds, not just the absence of noise.¹⁰²
Intervention Strategies:

Noise Reduction/Mitigation: Employing traditional techniques remains important where noise levels are problematic. This includes using noise barriers, optimizing road surfaces, managing traffic flow, designing building layouts to shield sensitive areas (creating quiet facades), and ensuring good sound insulation.¹⁶
Introducing Desired Sounds: Actively adding or enhancing sounds perceived positively:

Water Features: Fountains, cascades, streams can effectively mask traffic noise (effectiveness depends on feature type and noise level) and are generally perceived as pleasant and relaxing.¹⁶ Sound mapping can help determine optimal placement and type.¹²²
Natural Sounds: Promoting biodiversity through planting and habitat creation can increase desirable sounds like birdsong and rustling leaves.¹⁶ Strategic use of vegetation can also offer some acoustic screening.⁷⁹
Sound Art / Audio Installations: Purposefully designed installations (“audio islands”) can introduce specific sounds to shape perception, enhance identity, or mask unwanted noise.¹⁶

Sound Masking: Utilizing pleasant or neutral sounds (often water or specifically engineered sounds) to cover up or reduce the noticeability of less desirable sounds (like traffic or office chatter).²⁶ The masking sound must be contextually appropriate.²⁶
Acoustic Zoning and Quiet Area Management: Identifying zones with specific acoustic quality objectives and implementing measures to protect areas valued for their tranquility.⁶⁹ This includes designating and preserving “quiet areas” as mandated by the EU END, considering not just low dB levels but also perceived quality, accessibility, and greenness.⁶⁹
Urban Form and Materials: Considering how the shape, size, and layout of streets, buildings, and open spaces, as well as the choice of surface materials

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