PROCEEDINGS of the23rd International Congress on Acoustics
9 to 13 September 2019 in Aachen, Germany

The effect of spectral centroid on perceived birdsong in urbanforests
Xinchen HONG1, 2; Chen YAN1; Guangyu WANG2; Siren LAN1
1

Fujian Agriculture and Forestry University, China
2

University of British Columbia, CanadaABSTRACT
Probe into the relationship between spectral centroid and perception of birdsong in urban forests. Spectral
centroid (SC) and Spectral centroid bandwidth (SBW) were considered as potential factors affecting
perceived birdsong. In this study, we made the subjective evaluation of birdsong in three urban forested
area. In the meantime, we collected recordings at each observation site. Finally, through polynomial fitting,the relationship between the SC, SBW, and the pleasantness of perceived birdsong were found. Results
show that both of SC and SBW are potential factors and the latter is more important. The trends of SC andSBW with perceived birdsong is opposite.
Keywords: Perceived birdsong, Soundscape, Urban forests

1. INTRODUCTION
Urban forests are important habitats for birds and other animals to live, multiply and commute (1,2). Birds are well known and special communities in urban areas, distributed widely in urban forests(2, 3, 4). And the birds tend to produce birdsong for declaring the possession of territory andattracting mates, which could be more sensitive to the acoustic environment in urban forests (5, 6).
Moreover, birdsong could enhance perceived visual landscape and reduce noise pollution for citizens(7, 8, 9). The birdsong is the most desired soundscape in biophilic city and benefifits public healthbased on its pleasantness (10, 11, 12). Potential factors, such as spectral centroid, impacting onperception of birdsong are still being explored. Thus, this study aims to examine the potential effectof spectral centroid on perceived birdsong in urban forests.

2. METHOD
2.1 Study areas
The observation sites of this study are Jericho Beach Park, Stanley Park and Pacific Spirit Park.
These are important forested areas and all located in Vancouver, Canada. Jericho Beach Park (JB)
offers plenty of recreation opportunities located on the south side of English Bay, featuring areas oflawns and beaches for recreation and dog walking. Stanley Park (SP) is a world renowned urban park
located on a peninsula at the northwestern side of downtown Vancouver, with several beaches andwell-maintained paved and dirt trails. Pacific Spirit Regional Park (PP), located in the University
Endowment Lands area, has an endless number of trails with enormous logs and large woody debris
from decades of logging. Overall, there are a high level of forest cover and a strong attraction forvarious bird species in all the parks.
2.2 Procedure
A 5-point ordinal category scale was adopted to reply alternatives (13, 14, 15): For thepleasantness values, including “ not pleasantness at all (+1) ” , “ slightly pleasantness (+2) ” ,“moderately pleasantness (+3) ” , “ very pleasantness (+4) ” , and “extremely pleasantness (+5) ” . In
addition, while the participates assessed the perceived soundscape, the recordings of environment
12xch.hung@outlook.com
guangyu.wang@uba.ca

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were also recorded on a sound recorder.
The Experiments for gathering perceived soundscape information and recordings were conductedon sunny days except on holidays between 10:00 and 15:00 in February and March 2019. Previous
studies have shown that more than 7 trained participants are required to achieve sufficient andaccurate results (11, 16, 17, 18). Thus, 13 trained participants were selected at each park in this study,
aged 20-35 years old, with normal hearing to response to the questionnaires.

3. RESULT
3.1 Spectral centroid analysis
Spectral centroid (SC) and Spectral centroid bandwidth (SBW) describes the brightness andcentralized region of the sound through frequency contents (19, 20). The SC and SBW were obtained
from the recordings by Matlab R2018a.
Figure 1 and Figure 2 illustrates the SC and SBW situations in the urban forests. The variance ofSC in JP, SP, and PP ranged from 429.8 Hz to 800.8 Hz, 296.7 Hz to 1172.2 Hz, and 432.9 Hz to1067.9 Hz, respectively. The fluctuation of SBW in these parks ranged between 3256.4 Hz and7744.2 Hz, 2163.6 Hz and 7237.5 Hz, 2223.7 Hz to 5931.7 Hz. Although the three parks show
different frequency conditions for the SC, medians for SC are all greater than 500 Hz, indicating thatthe observation sites are more affected by high-frequency sound from birdsong. Also, medians for
SBW in these parks are all greater than 3.5k Hz, indicating that there are various birdsongs indifferent frequencies.

Figure 1 – Spectral centroid in JP, SP and PP

Figure 2 – Spectral centroid bandwidth in JP, SP and PP6690

3.2 The relationship between spectral centroid and pleasantness of perceived birdsong
Through polynomial fitting, the relationship between the SC, SBW, and the pleasantness ofperceived birdsong were plotted in Figure 3 and 4. There were opposite tendencies between SC withdecreasing trend and SBW with increasing trend. But there were some uncertain relations when theSC and SBW were lower than 689 Hz and higher than 5015.9 Hz, respectively. Furthermore, theresults suggest higher SC may lead to lower human ’ s perception of birdsong owing to increased
annoyance and masking affecting pleasantness of perceived birdsong.

Figure 3 – Polynomial fitting of SC and perceived birdsong

Figure 4 – Polynomial fitting of SBW and perceived birdsong

4. CONCLUSIONS
Birds are dominant creatures that produce abundant sounds in urban forests. Through tests in thisstudy, we found different frequency conditions for the SC and SBW in JP, SP and PP. Moreover,based on polynomial fitting between SC, SBW and perceived birdsong, we observed that both of SCand SBW are potential factors and the latter is more important. The trends of SC and SBW withperceived birdsong is opposite. Thus, the spectral centroid information may be considered in further
research, which will be beneficial to the perceived birdsong modelling.

ACKNOWLEDGEMENTS

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The authors would like to thank all participants who were involved in fieldwork for this study.
The PhD research of the first author is supported by the programme at Fujian Agriculture andForestry University that supports doctoral students to go abroad to be jointly trained. This project
was supported by the Funding of Engineering Research Center for Forest Park of National Forestry
and Grassland Administration, China (grant number PTJH1500217), and the Social Science
Foundation of Fujian, China (grant number FJ2018B087 and FJ2016C043).

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