Shiro Ise

Numerical study on source-distance dependency of head-related transfer functions

This paper investigates the source-distance dependency of head-related transfer functions (HRTFs) on the horizontal and median sagittal planes using the boundary-element method and a dummy head scanned with laser and computer tomography scanners. First, the HRTF spectra are compared among various source positions in a head-centered coordinate system, confirming that the major HRTF spectral features vary with source distance as stated in previous works. Furthermore, the HRTF spectra are compared in an ear-centered coordinate system, revealing how the outer ear angle of incidence affects the source-distance dependency of the HRTFs. Next, the comparison across coordinate systems reveals that the source-distance dependency of the ipsilateral HRTFs on the horizontal plane is mainly attributable to the outer ear angle of incidence, whereas the contralateral HRTFs vary with the source distance mainly due to the heads presence. Finally, results also show that, in an ear-centered coordinate system, the ipsilateral HRTFs do not depend strongly on a source distance greater than 0.2 m from the center of the head, whereas the contralateral HRTFs depend on source distance less than 1.8 m. Results also show that HRTFs on the median sagittal plane depend on a source distance of less than 0.4 m.

The Boundary Surface Control Principle and Its Applications

In order to control a sound field using multiple sources and microphones, we must choose the optimum values of parameters such as the numbers of sources and microphones, the location of the sources and the microphones and the filter tap length. Because there is a huge number of possible combinations of these conditions, the boundary surface control principle can be useful as a basis of a design method of such a system. In this paper, a design method of sound field reproduction and active noise control based on the BSC principle are described and several example of its application are presented.

Design and collection of acoustic sound data for hands-free speech recognition and sound scene understanding

The sound data for open evaluation is necessary for studies such as sound source localization, sound retrieval, sound recognition and hands-free speech recognition in real acoustic environments. This paper reports on our project for acoustic data collection. There are many kinds of sound scenes in real environments. The sound scene is specified by sound sources and room acoustics. The number of combinations of the sound sources, source positions and rooms is huge in real acoustic environments. We assumed that the sound in the environments can be simulated by convolution of the isolated sound sources and impulse responses. As an isolated sound source, hundred kinds of environment sounds and speech sounds are collected. The impulse responses are collected in various acoustic environments. Additionally we collected sounds from a moving source. In this paper, progress of our sound scene database collection project and application to environment sound recognition and hands-free speech recognition are described.

Development and application of induced-strain actuators for building structures

Induced strain actuator (ISA) can change their own shapes according to external electric/magnetic fields, and vice versa. Recently these materials have been widely used for the small/precision. The objectives in this study are to develop smart members for building and to realize the smart, comfortable and safe structures. The research items are 1) Semi-active isolation of structures using piezoelectric actuator, 2) Using ISA as sensor materials and 3) Improvement of Acoustic Environment. Semi-active base isolation system with controllable friction damper using piezoelectric actuators is proposed. Simulation study was carried out, and by semi-active isolation, it could be realized to reduce response displacement of the structure to 50% of values of the passive isolation. ISA materials can act as sensors because they cause change of electric or magnetic fields under deformation. PVDF sensors are suitable for membrane structures. We evaluate performance of PVDF sensors for membrane structures by experiment. Polymer based ISA films or distributed ISA devices can control vibration mode of plane members. Applications to music halls or dwelling partition walls are expected. Results of experimental studies of noise control are discussed.

3-D sound reproduction system for immersive environments based on the boundary surface control principle

We constructed a 3-D sound reproduction system containing a 62-channel loudspeaker array and 70-channel microphone array based on the boundary surface control principle (BoSC). The microphone array can record the volume of the 3-D sound field and the loudspeaker array can accurately recreate it in other locations. Using these systems, we realized immersive acoustic environments similar to cinema or television sound spaces. We also recorded real 3-D acoustic environments, such as an orchestra performance and forest sounds, by using the microphone array. Recreated sound fields were evaluated by demonstration experiments using the 3-D sound field. Subjective assessments of 390 subjects confirm that these systems can achieve high presence for 3-D sound reproduction and provide the listener with deep immersion.

Subjective evaluation of a virtual acoustic system: Trials with three-dimensional sound field reproduced by the “Sound Cask”

It has been necessary to establish subjective measures for the performance of the virtual acoustic systems. In this paper, we report our trials to evaluate the performance of a three-dimensional sound field reproduction system based on the boundary surface control principle, the “Sound Cask.” First, we introduce our investigations for the experts of audio engineering in order to clarify the difference of auditory impression between the Sound Cask and conventional audio systems. Second, we report psychological and physiological experiments focusing on the advantageous points of the Sound Cask, localization performance, and a clear sense of reality, which were pointed out in the investigations for the experts. Finally, we discuss the issues to be considered for subjective evaluation of virtual acoustic systems for future studies.

Providing immersive virtual experience with first-person perspective omnidirectional movies and three dimensional sound field

Providing high immersive feeling to audiences has proceeded with growing up of techniques about video and acoustic medias. In our proposal, we record and reproduce omnidirectional movies captured at a perspective of an actor and three dimensional sound field around him, and try to reproduce more impressive feeling. We propose a sequence of techniques to archive it, including a recording equipment, video and acoustic processing, and a presentation system. Effectiveness and demand of our system has been demonstrated by ordinary people through evaluation experiments.

Three-dimensional remote ensemble system using the immersive auditory display “Sound Cask.”

A 3D sound field simulation system using the immersive auditory display system, “sound cask,” has been developed for creating a virtual environment that would reproduce the 3D acoustics of concert halls for musicians. The simulation system is based on the boundary surface control principle. The original sound field was measured using a microphone array consisting of 80 omnidirectional microphones installed at the nodes of the C80 fullerene structure. The virtual sound field was then constructed in a cask-shaped space (approx. 2 × 2 m), with 96 channel full-range loudspeakers installed in the space. The 3D acoustic waves of music, including the acoustic condition on the stage, were created virtually inside the sound cask. For this, the first step was to design inverse filters of the MIMO system between the 96 loudspeakers and 80 microphones located in the sound cask. Next, the inverse filters and the impulse responses measured in actual concert halls and signals from instruments played by musicians were co...

Synthesis of wave front in the sound field recording/reproduction system based on the boundary surface control principle

Based on the boundary surface control (BSC) principle, a new recording/reproduction system is developed to realize high fidelity three-dimensional sound field reproduction. Theoretically, by using this new system, physically faithful reproduction could be achieved in any acoustic environments. Sound recording/reproduction systems based on the BSC principle require many loudspeakers and many microphones. In this new system, the microphone array system to record 3D sound field consists of 70 microphones, and the loudspeaker system to reproduce the recorded 3D sound field consists of 62 full-range units and 8 sub-woofer units. To evaluate the ability of this system, the wave front which is measured in the soundproofed room is compared with the reconstructed wave front within this system. The experiment shows that the reconstructed secondary wave front is very similar to the primary wave front in lower frequency.

Numerical calculation method of binaural signals suitable for auralization of a reflective sound field

Based on the Kirchhoff‐Helmholtz integral equation, a numerical calculation method, which enables a wave‐theory‐based auralization of a sound field inside room, is proposed. Binaural signals are synthesized from pressures and particle velocities on the boundary surface and corresponding head‐related transfer functions (HRTF). The proposed method can shorten the extra computation time that is required because of changes in numerical conditions caused by head movement and rotation. The boundary element method (BEM) was used to calculate surface values on sound‐reflective objects. In addition, HRTFs for various source positions were calculated using a BEM‐based HRTF calculation system [M. Otani and S. Ise, J. Acoust. Soc. Am. 119, 2589–2598 (2006)]. Results obtained using the proposed method are compared with those of the conventional BEM, whose boundary consists of a head and a wall, and an image source method, which does not incorporate sound wave motion. Those comparisons reveal that the proposed method c...