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Psychoacoustics and Its Benefit for the Soundscape

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Psychoacoustics and Its Benefit for the Soundscape ACTA ACUSTICA UNITED WITH ACUSTICA Vol. 92 (2006) 1 – 1 Psychoacoustics and its Benefit for the Soundscape Approach Klaus Genuit, André Fiebig HEAD acoustics GmbH, Ebertstr. 30a, 52134 Herzogenrath, Germany. [klaus.genuit][andre.fiebig]@head- acoustics.de Summary The increase of complaints about environmental noise shows the unchanged necessity of researching this subject. By only relying on sound pressure levels averaged over long time periods and by suppressing all aspects of quality, the specific acoustic properties of environmental noise situations cannot be identified. Because annoyance caused by environmental noise has a broader linkage with various acoustical properties such as frequency spectrum, duration, impulsive, tonal and low-frequency components, etc. than only with SPL [1]. In many cases these acoustical properties affect the quality of life. The human cognitive signal processing pays attention to further factors than only to the averaged intensity of the acoustical stimulus. Therefore, it appears inevitable to use further hearing-related parameters to improve the description and evaluation of environmental noise. A first step regarding the adequate description of environmental noise would be the extended application of existing measurement tools, as for example level meter with variable integration time and third octave analyzer, which offer valuable clues to disturbing patterns. Moreover, the use of psychoacoustics will allow the improved capturing of soundscape qualities. PACS no. 43.50.Qp, 43.50.Sr, 43.50.Rq 1. Introduction disturbances and unpleasantness of environmental noise, a negative feeling evoked by sound. However, annoyance is The meaning of soundscape is constantly transformed and sensitive to subjectivity, thus the social and cultural back- modified. The inflationary use of this term refers to the grounds have an important influence on the subjective at- large diversity of interpretations with respect to the content titudes of people to noise [4] and they must be consid- of the soundscape idea – making it impossible to present a ered besides physical parameters. Therefore, the complex- general acknowledged definition. Often, the institutional ity of noise annoyance and the description of soundscapes, and disciplinary backgrounds of the researchers have a which means more than only the determination of annoy- sustainable effect on their soundscape concept. Schafer, a ance, cannot be simply described with a single parame- “soundscape pioneer”, describes the vital question in this ter, because many factors contribute to it. Hence, individ- context: ”What is the relationship between man and the ual, contextual or physical variables, causing a deviation sounds of his environment [. ]? [. ] Only a total appreci- from the “law of averages” implied by dose-response rela- ation of the acoustic environment can give us the resources tionships, must be determined with respect to an improved for improving the orchestration of the world soundscape” understanding of annoyance as caused by environmental [2]. A soundscape is not an objectively existing reality noise [5]. (you cannot overflow the soundscape and take a picture), Psychoacoustics will make a meaningful contribution to but it is a culturally-affected environment constituted by it and will allow the detection of specific soundscape fea- human perception [3]. tures. Today, environmental noise is calculated and depicted in noise-maps with the A-weighted sound pressure level 2. Psychoacoustics in soundscape research (SPL). Those noise maps neglecting the specific charac- ter of a soundscape are often the basis for discussions and 2.1. Psychoacoustics and soundscapes interpretations regarding noise annoyance. In this context, it is necessary to reflect also the meaning of annoyance. Psychoacoustics covers one important field of the differ- Annoyance will be used here as an overall evaluation of ent dimensions involved in the environmental noise eval- uation process. It describes sound perception mechanisms in terms of several parameters, such as loudness, sharp- Received 1 January 2005, ness, roughness, and fluctuation strength as well as further accepted 1 January 2005. hearing-related parameters. © S. Hirzel Verlag · EAA 1 ACTA ACUSTICA UNITED WITH ACUSTICA Genuit, Fiebig: Psychoacoustics in soundscape research Vol. 92 (2006) Soundscape is used as the complex superposition of 2.2. The application of psychoacoustics in the con- natural, human and technical (emitting from machinery text of environmental noise or electroacoustic reproduction devices) noises and their perception. Soundscapes consist of a number of spatially Different calculation methods and models, which, accord- distributed sound sources, which give the soundscapes ing to the rule of distance for SPL reduction, and by tak- their distinctive features. The emitted noise of each source ing into account propagation properties, reflections against could be measured and analyzed in terms of several pa- objects, damping factors, are an attempt in predicting how rameters. However, the annoyance due to given individ- A-weighted SPL evolves as a function of distance, how- ual sound sources cannot be transferred to the overall an- ever, neglecting time and frequency information. In real- noyance of an entire, complex soundscape containing the ity though, the calculated LAeq and the expected corre- noise of different sound sources, because of e.g. masking sponding noise annoyance, often differ widely from the effects [6]. evaluations made by the concerned residents [11]. This ex- plained with the fact that the human hearing, in contrast to Surveys have documented that spatiality plays an im- a sound level meter, is not an absolute measuring instru- portant role for physiological reactions and annoyance. In ment. It shows a differentiated sound perception due to its the context of industrial noises, a study has investigated non-linearity and adaptivity as well as its signal process- the influence of the direction of sound incidence (uni- ing characteristics, paying attention to further factors than directional, multi-directional) on physiological reactions only to the averaged intensity of the sound event [12]. and loudness evaluation. It could be observed that the re- It could be established that the time structure of occur- action to the multi-directional situation was higher than rence of sound events in the context of traffic noise has the reaction to the uni-directional situation, although both a major influence on the noise annoyance. A high traf- noise situations produced the same SPL at the position of fic load noise can be evaluated as more pleasant than low the listener [7]. Therefore, the spatial distribution of sound traffic load noise because of the perceivable single vehicle sources as well as the direction and speed of any move- pass-by’s penetrating the quietness, which “startled” per- ment of these sources can be relevant for the perception manently the exposed persons. For example, traffic noise and evaluation of environmental noise. was measured and analyzed for the understanding of exte- In fact, the determination of noise annoyance caused by rior vehicle noise perception and resulting effects on man complex sound situations arising from the superposition in the European research project “Sound Quality of Exte- of the emitted sounds by a number of sources is very com- rior Vehicle Noise” (SVEN). There, traffic noise recorded plicated and the (binaural) signal processing involved in in L-shaped and U-shaped streets was analyzed and eval- human hearing has to be considered. The use of aurally- uated. The noise for the “L-shaped building” street was accurate measurements provides the opportunity to con- judged by the majority to be a bit or much louder and more sider binaural signal processing phenomena. dangerous, unpleasant and annoying compared with the U- The fact, that annoyance resulting from the listener’s shaped street. With respect to the general judgements the surrounding soundscape is also depending on the personal “L-shaped building” traffic noise was again judged less attitude of the listener, further increases the intricacy of the fa vourable. Therefore, the street shape – U-shaped, L- soundscape approach, which has to integrate important as- shaped – affects also the noise situation (because of dif- pects, such as the physical situation, experience and inter- ferent reflection patterns and time structure) and the noise pretation of the environment into one broad concept [8]. annoyance respectively [13]. Even visual information of the location affects noise eval- Another ongoing European research project is “Quiet uation [9]. Abe et al. concluded that the influence of visual City Transport” (QCity), which underlines the endeavour and verbal information on the auditory evaluation of envi- to further explore the connection between urban noise and ronmental sounds is considerable [10]. In order to capture its perception and evaluation [14]. It was observed that the mentioned difficulties with respect to human sensation many hot-spots regarding complaints cannot be explained and evaluation of environmental noise, the transformation with data from noise maps alone. The LAeq does not suf- of a sound event (the physical situation) into the perceived ficiently describe the environmental noise and its percep- sound event has to be considered. This transformation is tion. influenced by different aspects: first of all, the physical as- Figure 1 illustrates the behaviour of different parame- pect; secondly, the psychoacoustic
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