Psychophysiological Evidence of an Autocorrelation Mechanism in the Human Auditory System

This article details a model for evaluations of sound quality in the human auditory system. The model includes an autocorrelation function (ACF) mechanism. Thus, we conducted physiological and psychological experiments to search for evidence of the ACF mechanism in the human auditory system. To evaluate physiological responses related to the peak amplitude of the ACF of an auditory signal, which represents the degree of temporal regularity of the sound, we used magnetoencephalography (MEG) to record auditory evoked fields (AEFs). To evaluate psychological responses related to the envelope of the ACF of an auditory signal, which is a measure of the repetitive features of an auditory signal, we examined perceptions of loudness and annoyance. The results of the MEG experiments showed that the amplitude of the N1m, which is found above the left and right temporal lobes around 100 ms after stimulus onset, was a function of the peak amplitude and its delay time or the degree of envelope decay of the ACF. The results of the psychological experiments indicated that loudness and annoyance increased for sounds with envelope decay of the ACF in a certain range. These results suggest that an autocorrelation mechanism exists in the human auditory system

Effects of Platform Screen Doors on Sound Fields in Underground Stations

This chapter investigates the acoustic effects of platform screen doors (PSDs) in underground stations using computer simulation and scale model testing. The dimensions of underground stations with island and side platforms were determined based on a field survey. Ray-tracing-based computer models and 1/25 scaled-down physical models of these underground stations were used to simulate their sound field characteristics. In the experiments, five types of PSDs were tested: mobile closed full-height (MCFH), mobile open full-height (MOFH), mobile half-height (MHH), fixed half-height (FHH) and fixed barrier (FB) doors. Four acoustic parameters, namely, speech intelligibility, sound pressure level, reverberation time and the inter-aural cross-correlation coefficient were used to understand the sound field characteristics from the sound source of public address announcements. It was found that speech intelligibility and the sound pressure level were increased by most types of PSDs apart from the MCFH. The MOFH showed the highest levels of speech intelligibility and spatial diffusivity. In addition, the noise reduction effects of PSDs for train noise were discussed. PSDs on side platforms showed higher noise reduction performances than PSDs on island platforms. The specific noise reduction levels for the MOFH type were 4.3 dB on island platforms and 5.0 dB on side platforms

An Exploratory Analysis of Sound Field Characteristics using the Impulse Response in a Car Cabin

Sound environments in cars are becoming quieter and receiving attention because of the prevalence of low-noise engines such as hybrid and electric engines and the manifestation of automated driving. Although the car cabin has potential as a listening space, its acoustic quality has not been examined in detail. The present study investigated sound field characteristics in the car cabin using acoustic parameters obtained by impulse response analysis. In particular, effects of the passenger position, open windows and the use of an air conditioner on acoustic parameters were investigated. The passenger position affected the sound strength at low frequencies. Rear seats, except for the rear central seat, had lower interaural correlation than the front seats, suggesting that rear seats have more diffused sound fields. The opening of windows and use of air conditioners attenuated the ratio of early- and late-arriving energy at high frequencies, suggesting a loss of clarity for music

Subjective Salience of Birdsong and Insect Song with Equal Sound Pressure Level and Loudness

Birdsong is used to communicate the position of stairwells to visually impaired people in train stations in Japan. However, more than 40% of visually impaired people reported that such sounds were difficult to identify. Train companies seek to present the sounds at a sound pressure level that is loud enough to be detected, but not so loud as to be annoying. Therefore, salient birdsongs with relatively low sound pressure levels are required. In the current study, we examined the salience of different types of birdsong and insect song, and determined the dominant physical parameters related to salience. We considered insect songs because both birdsongs and insect songs have been found to have positive effects on soundscapes. We evaluated subjective saliences of birdsongs and insect songs using paired comparison methods, and examined the relationships between subjective salience and physical parameters. In total, 62 participants evaluated 18 types of bird songs and 16 types of insect sounds. The results indicated that the following features significantly influenced subjective salience: the maximum peak amplitude of the autocorrelation function, which signifies pitch strength; the interaural cross-correlation coefficient, which signifies apparent source width; the amplitude fluctuation component; and spectral content, such as flux and skewness

Neurally based measurement and evaluation of environmental noise

This book deals with methods of measurement and evaluation of environmental noise based on an auditory neural and brain-oriented model. The model consists of the autocorrelation function (ACF) and the interaural cross-correlation function (IACF) mechanisms for signals arriving at the two ear entrances. Even when the sound pressure level of a noise is only about 35 dBA, people may feel annoyed due to the aspects of sound quality. These aspects can be formulated by the factors extracted from the ACF and IACF. Several examples of measuring environmental noise—from outdoor noise such as that of aircraft, traffic, and trains, and indoor noise such as caused by floor impact, toilets, and air-conditioning—are demonstrated. According to the noise measurement and evaluation, applications for sound design are discussed. This book provides an excellent resource for students, researchers, and practitioners in a wide range of fields, such as the automotive, railway, and electronics industries, and soundscape, architecture, and acoustics