32-channel Microphone Array Research Articles

An open-source spherical microphone array design

We present an open-source design for producing a spherically baffled, 32-channel microphone array having elements aligned with the vertices and face centers of a dodecahedron, and fabricated using additive manufacturing (3-D printing). The design approach emphasized low cost, assembly ease, and acoustic integrity. Mechanical, electrical, and acoustical design considerations are discussed, as are assembly and calibration details. The baffle is a 10-cm-radius sphere, built from separable hemispheres, and supported by a 2-cm-diameter cylindrical stand that serves as a conduit for the microphone signal cables. Microphone capsules are mounted on preamp boards, which provide balanced line level outputs, and press fit to the baffle. The performance of the array is characterized, and an example application to spatial room impulse response measurement is provided. Design documents, including the enclosure model and preamp electrical design and board layout, are provided at https://ccrma.stanford.edu/~granzow/sphericalmicarray/

High resolution radiation pattern measurements of a grand piano—The effect of attack velocity

The sound radiation pattern of a grand piano is highly complex and depends on the shape of the soundboard, construction of the frame, reflections from the lid, and other parts of the instrument’s structure. The spectral energy generated by and emitted from the instrument is further complicated by the sound production mechanism (hammers, strings), the attack velocity, and results in independently complex behaviors depending on the register of the piano. This paper presents the acoustic measurements of the radiation pattern of a grand piano using a high spatial resolution measurement technique. Measurements of a Yamaha Diskclavier were taken using a 32-channel microphone array with a 2-in. spacing between capsules. The complex radiation patterns and overtone structure is analyzed for middle-C at three attack velocities—pianissimo, mezzo forte, and forte. Comparisons of the effect of attack strength on frequency response and radiation pattern are presented.

Pitch-Cluster-Map Based Daily Sound Recognition for Mobile Robot Audition

This paper presents a sound identification method for a mobile robot in home and office environments. We propose a short-term sound recognition method using Pitch-Cluster-Maps (PCMs) sound database (DB) based on a Vector Quantization approach. A binarized frequency spectrum is used to generate PCMs codebook, which describes a variety of sound sources, not only voice, from short-term sound input. PCMs sound identification requires several tens of milliseconds of sound input, and is suitable for mobile robot applications in which conditions are continuously and dynamically changing. We implemented this in mobile robot audition system using a 32-channel microphone array. Robot noise reduction and sound source tracking using our proposal are applied to robot audition system, and we evaluate daily sound recognition performance for separated sound sources from a moving robot.

Experimental measurements of turbulent boundary layer flow over a square-edged rib

Abstract Statistical turbulence properties of turbulent flow over a two-dimensional rib which was flush mounted on a wind tunnel wall was extensively surveyed. Velocity fluc- tuations in the turbulent separated and reattaching flow and wall-pressure fluctuations on the rib and its downstream surface were obtained by using a split-fiber hotwire anemometry and a 32-channel microphone array, respectively. Distribution of the wall static pressure was acquired by using a Scanivalve system. Statistical quantities of the turbulent separated and reattaching flow were determined in terms of wall static pressure distri- bution, profiles of the streamwise velocity and its fluctuations, wall pressure fluctuation coefficient, and wall-pressure spectra. Characteristics of the shedding large-scale vortical structures buried in the turbulent flow were disclosed.

A noise‐robust speech input interface for information kiosk terminals

AbstractIn social amenity apparatus such as information terminals or on‐line shopping terminals and ticket vending machines, more natural and smoother communication between machines and humans is made possible by incorporating speech recognition, thus rapidly enhancing operation and convenience. In this paper, we will describe the trial production of an information kiosk terminal equipped with speech recognition and the noise reduction technique adopted as a speech input interface. In general, the aforementioned system equipment is installed in public spaces such as stations. Therefore, robust speech recognition performance is required even in the worst noise environments. For the realization of this antinoise capability, we have used noise reduction based on both a microphone array and spectral subtraction (SS). Experiments with evaluation data recorded in real environments indicate that a recognition performance of over 90% in isolated‐word recognition of 216 words uttered by an unspecified speaker is achieved by the combined use of a 32‐channel microphone array and SS. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 87(12): 51–61, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.20135

Three-dimensional coherent structure in a separated and reattaching flow over a backward-facing step

An experimental study was carried out to elu- cidate the large-scale vortical structure in a separated and reattaching flow over a backward-facing step. The Rey- nolds number based on the step height (H) was ReH=33,000. The large-scale vortical structure was probed by means of three-dimensional velocity measurements performed at the recirculation zone (x/H=4.0) and the reattachment zone (x/H=7.5). A 32-channel microphone array extending in the streamwise and spanwise directions was used for sensing the wall pressure fluctuations. The relationship between the flow field and the relevant spatial mode of the pressure field was determined by examining the spatial box filtering. From the relevant spatial mode of the wall pressure fluctuations, a conditional averaging technique was employed to characterize the coherent structure. In addition, the cross-correlation between velocity and wall pressure fluctuations was calculated to identify the structure and the length scale of the large-scale vortex. The cross-correlation results revealed that the large-scale hairpin vortices have a three-dimensional structure, in agreement with previous findings. The pres- ent results clearly show the growth and downstream elongation of the hairpin vortices. List of symbols H step height, m k turbulent kinetic energy, m 2 /s 2 q freestream dynamic pressure, Pa ReH Reynolds number based on U0 and H,UoH/m U0 freestream velocity, m/s Uc convection velocity, m/s X0 streamwise coordinate of the measurement origin, m xR time mean reattachment length, m

후향계단 난류 박리재부착 유동에서의 대형와의 구조

An experimental study was made of a large-scale vortical structure over a backward-facing step. The Reynolds number based on the step height was Re_H =33,000. To recognize the large-scale vortex, three components of velocity were measured. The measurements were performed in the recirculation zone (x/H=4.0) and the reattachment zone(x/H=7.5). To measure the wall pressure fluctuations in a turbulent flow over a backward-facing step, a 32-channel microphone array was installed beneath the wall in the streamwise and spanwise directions. From the measured pressure field, the size of large-scale vortex was obtained. As a detailed study, a conditionally-averaging technique was employed to characterize the coherent structure of the large-scale vortex. To see the relationship between the flow field and the relevant spatial mode of the pressure field, the spatial box filtering (SBF) was examined. A cross-correlation between velocity and pressure fluctuations was performed to identify the structure and the length scale of the large-scale vortex.