Mapping Urban Soundscape in 4D

05/31/2023

1. What is soundscape

As defined by International Organization for Standardization (ISO), “soundscape” is the acoustic environment as perceived, experienced, or understood by a person (ISO, 2014), and is rooted in the music and acoustic ecology research areas (Schafer, 1993). The soundscape is different from the acoustic environment as the former refers to a perceptual construct, and the latter to physical measurements of sound. The soundscape is more comprehensive, and includes the acoustic environment as well as interrelationships between persons, activities, spaces, and time. It is a research area where a human being is the key element, concerning disciplines such as architecture, urban study, psychology, and sociology.

Soundscape is the acoustic environment as perceived, experienced, or understood by a person.

2. Why soundscape matters

There are four reasons for creating soundscape maps for our cities:

2.1 Experiencing environment through multiple sensations

Human beings integrate information collected through different sensations. Spaces and urban environments cannot be described, appreciated, and consequently valorized using a mono-sensorial component analysis essentially based on vision (Kang et al., 2016). We use Google Maps, Apple Maps, and Baidu Maps to orient ourselves, find locations, and navigate through space. These maps provide geographic information, with street views providing a visual representation of space. Soundscape maps provide a novel way of experiencing space.

2.2 Influencing human mental status

First, Attention Restoration Theory posits that our top-down attention, which becomes depleted through mentally demanding tasks associated with everyday life, can be restored through exposure to natural settings (Kaplan, 1995; Sullivan & Li, 2021). Natural visual and acoustic stimuli engage our bottom-up attention, thus allowing our top-down attention a chance to recover from the mental fatigue associated with modern life (Kaplan, 1995).  

Second, our well-being is influenced by the sounds we are exposed to natural sound (wind, birds, trickling water) and can have a positive influence on attention restoration and promote positive mood (Benfield et al., 2014). Whereas anthropogenic sounds (traffic noise, horn, construction, mechanical equipment vibrant) is associated with negative mental health symptoms and psychological disorders such as depression and anxiety (Hahad et al., 2019).

Third, the soundscape is related to the socio-cultural background. It can stimulate our sphere of emotions and they can influence our global sensation in experiencing that specific context (Burgess, & Wathey, 2000). The pleasantness and eventfulness are two attributes that refer to the emotional magnitude of the sound perception (Erfanian, Mitchell, Kang, & Aletta, 2019). The meanings of sound, the composition of diverse sound sources, and the visual-acoustic interaction are all unique components related to the experience of certain soundscapes. Well-planned soundscapes can promote performance, improve well-being, and evoke emotion and memory.

2.3 Creating new signs of identity of a space / a city

In urban studies, a landmark is defined as an external point of reference that helps to orient in a familiar or unfamiliar environment (Lynch, 1960). Most of the metropolitans have buildings, status, or other forms of built structure as landmarks. On a smaller scale, a district, or a neighborhood can have unique objects to identify themselves. Soundscapes contains certain context and can also be used to assign a new identity to a space or a city. For example, the acoustic effect in train stations, the horn on the street, and church bells.

2.4 Preserving historic heritage

The soundscape of important scenarios should be considered intangible cultural elements, linked to the social and cultural heritage of the community and part of our history (Kang et al., 2016). The processes of globalization and new technologies can change the urban soundscape. Considering soundscape as one scale of the evolution of society, mapping the soundscape is documenting the development of the city.

2.5 Feeding data to the IoT (Internet of Things) network

The same as surveillance cameras, the sound recording device can also be a tool of the “Internet of Things” (IoT) to collect spatial data for research, policy-making, commercial development purpose, meditation, recreation, etc.

3. Existing work of soundscape maps

There are several soundscape maps designed with different ways of collecting sound, categorizing sound, and interface interaction.

3.1 Hush City

Hush City (Hush City Lab, 2017) focuses on mapping quiet areas around the world through a mobile app. Users can write/read feedback and upload/browse any photographs of the location posted to Hush City. The color of a marker indicates the noise levels measured at a location by the app, shown in A-weighted decibels (an expression of the relative loudness of sounds as perceived by the human ear).

3.2 Earth.fm

Earth.fm (Earth.fm, 2018) is a map featuring the sounds of nature captured by professionals across the world. The sound clips collected are grouped into various categories based on the recording environment, and effects on human perception. Users can navigate through the website or create a web extension to play the soundscape.

3.3 Cities and Memory

The Cities and Memory (Cities and Memory, 2015) sound art project aims to present both the real sounds of the world and also their re-imagined counterparts, creating two parallel sound worlds: one of the real world and one of the imaginary. Every location and every faithful field recording on the Cities and Memory sound map is accompanied by a reworking, a processing, or an interpretation that imagines that place and time as somewhere else.

4. Four dimensions of a soundscape map

The present work proposes creating a soundscape map organized by human beings’ mental perception with geographic information and virtual effect. In the map, four dimensions -- sound marks, geographic information, human perception, and time flow are used to measure the soundscape.

4.1 Sound marks

Environmental sound by definition is not the primary focus of attention of a person submerged in it. Rather, specific sounds that stand out, that are salient, attract attention and become auditory objects as the listener starts paying attention to them (Botteldooren et al., 2015).

4.2 Geographic information

Geographic information provides information relevant to location, climate, and context. It gives a sense of orientation and relates to certain spatial experiences.

4.3 Human perception

Human beings’ perception, processing, and understanding make acoustic situations into soundscapes. In the map, people’s mental activity will be used to categorize different soundscapes.

4.4 Time flow

The soundscape of a space or urban area change dynamically a different time. One example is a commercial street that has diverse sounds like human talks, and traffic noise, but can be silent at nighttime. This determines the soundscape map needs to reflect the change of soundscape in time.

5. Parameters and evaluation method to use in soundscape map

5.1 Objective psychoacoustic parameters

There are four international general main objective psychoacoustic parameters to be tested:

Loudness -- describes the degree of psychological perception of sound in the hearing. The main methods to calculate the complex noise loudness were independently developed (Stevens & Zwicker, 2017). The former is suitable for the diffusing sound field, whereas the latter fits the diffusion and free sound field conditions.

Sharpness -- represents the auditory perception related to the spectral correlation of the sound

Roughness -- reflects the auditory perception characteristic related to the frequency modulation, amplitude modulation, and sound level for the sound with a frequency of 20–200 Hz. (Aures, 1985).

Fluctuation strength -- suitable for the evaluation of sound signals for low-frequency modulation below 20 Hz; it reflects the relief intensity of loudness for the subjective feeling of ears.  (Zwicker and Fastl, 1999).

5.2 Subjective evaluation

Different from maps that focus on geographic information, the soundscape map organizes the collection of sounds according to people’s cognition/experience of the sound. Under this circumstance, the evaluation and characterization of soundscape need to be done based on human perception.

Some studies proposed to assess soundscape using general descriptors for “soundscape quality”, addressing the overall perception of the acoustic environment, i.e., measuring whether a soundscape is “good” or “bad” (Aletta et al., 2016), “quite” or “loud”, “natural” or “non-natural”. There are parametrical models commonly used to quantify sound quality, the semantic differential method, and the paired comparison method (Jiang & Li, 2018). However, the perception of certain pieces of sound varies individually. Some studies have been done to learn the correlation between sound evaluation and factors like gender (Yang & Kang, 2005), education level (Miedema & Vos, 1999), general state of health, economic status (Fields, 1993), etc. Effects like exposure to noise, behavior, and habit are actives are highly related to sound evaluation.

5.3 Fuzzy logic

The assessment of urban soundscapes is quite complex and many factors come into play (Rey et al., 2015). In this soundscape map, the sound is not evaluated or labeled with certain subjective descriptions. The network of soundscape intends to help people navigate through their mental status and demand. A fuzzy cognitive framework is applied to map the characteristics of the soundscape.

Fuzzy logic is intended to model logical reasoning with vague or imprecise statements (Cintula et al., 2023). One of the goals of fuzzy logic is to emulate the way humans’ reason, which is typically by imprecise rules and common sense (Rodrigo, 2020). A fuzzy-logic-based equalizer for musical genres was proposed by incorporating significant audio descriptors that allow for the recognition and description of diverse musical genres ( Rey et al., 2015) . There is research about soundscape quality analysis using fuzzy logic (Maristany et al, 2016) . A music recommendation system is created based on a fuzzy inference engine that considers user activities and emotions as part of the recommendation parameters ( Kasinathan et al, 2019).

Formally, a fuzzy rule is a conditional of the form IF X is A THEN Y is B, where A and B are fuzzy sets (Kosko, 1993). Typically, fuzzy systems contain a large rule base and the method by which the computation of the contribution of each rule is achieved is known as aggregation. In this research, Mamdani method, proposed in 1975 by Mamdani and Assilian (Ross, 2010).

After inference, there comes defuzzification, a process to which several approaches exist (Ross, 2010). One of the most used ones is the centroid method, where the center of mass of the aggregated fuzzy output is computed as a scalar value.

6. Planned equipment

A large amount of study has been done to study acoustic topics. Binaural recording devices (Rey et al., 2015), and Microphone (Woodcock et al., 2017) are used to record sound. Some soundscape mapping projects, like Hush City (Hush City Lab, 2017) use personal mobile devices to record and upload sound records. Earth.fm (Earth.fm, 2018) records and curates’ soundscapes by professional field recordists. In this research, a sound recording modular integrated into urban infrastructures is proposed to capture soundscape in different urban settings, for example, city parks, transit stations, street crosses, public plazas, restaurants, tourism spots, etc. The challenges of collecting soundscape information are privacy issues and copyright violations. While deploying the recording device, people in the scope of the recording should be noticed.


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