Showing papers on "Microphone array published in 1988"

A microphone array with adaptive post-filtering for noise reduction in reverberant rooms

Abstract: The author presents a self-adapting noise reduction system which is based on a four-microphone array combined with an adaptive postfiltering scheme. Noise reduction is achieved by utilizing the directivity gain of the array and by reducing the residual noise through postfiltering of the received microphone signals. The postfiltering scheme depends on a Wiener filter estimating the desired speech signal and is computed from short-term measurements of the autocorrelation and cross-correlation functions of the microphone signals. The noise reduction system has been tested experimentally in a typical office room. The system produces an enhanced speech signal with barely noticeable residual noise if the input SNR is greater than 0 dB. The received noise power-measured in the absence of the speech signal-can be reduced by 28 dB. >

Sound source search instrument

Abstract: PURPOSE:To enable a sound image and an object image to be accurately overlapped and displayed by arranging a microphone array and an object image sensing device on the mirror axis of a sound collector with the focal planes of both the array and the device close to each other. CONSTITUTION:A reflecting surface 1a for reflecting a noise from a sound source object is formed on the concave curved surface of a sound collector 1. A microphone array 2 wherein microphones constituting a focal plane for forming a sound image thereon are arranged in matrix is arranged opposite to the reflecting surface 1a. A TV camera 6 that constitutes an object image sensing device for sensing the sound source object is mounted on the bracket 5 on the back of the distributing box 4 of the microphone array 2 while being directed to the sound source object. Thus, by mounting the TV camera 6 to the back of the distribution box 4, the microphone array 2 that is a focal plane on which the sound image is formed and the focal plane of the TV camera 6 are positioned close to each other. Accordingly, even though the microphone array 2 is moved for focusing in accordance with a distance between the sound collector 1 and the sound source object, a difference is scarcely generated in the field angle of the TC camera 6.

Real‐time visualization of acoustic wave fronts by using a two‐dimensional microphone array

Abstract: This article describes a real‐time visualization system for sound fields. The system includes a two‐dimensional microphone array (8×8), which eliminates the need for mechanically scanning the microphone and enables real‐time processing. Three methods are tested for drawing interpolated images of sound fields from the sparse sampling points. A frequency‐detection circuit is introduced to show the direction of sound propagation stroboscopically. Superposition of visualized sound wave fronts on the video picture of the field helps one to understand the sound fields present.

Adaptive microphone array system for noise reduction (AMNOR) and its performance studies

Abstract: The author describes the principle and performance of AMNOR, which consists of a compact microphone array and signal processing techniques that include an adaptive filter. It achieves high-SNR (signal-to-noise) sound reception, which is essential in areas such as teleconference systems and speech-recognition systems. The basic distinction of AMNOR compared to previous designs is that it realizes higher SNR by accepting some degree of degradation of a desired speech signal. A noise power minimization problem under second-order constraints is solved in the AMNOR system using an adaptive filter. An experiment conducted in an ordinary room showed that AMNOR realized a 21-dB SNR improvement, while a conventional directional microphone attained a 3-dB SNR improvement. >

Signal Restoration of Non-stationary Acoustic Signals in the Time Domain

Abstract: Signal restoration is a method of transforming a nonstationary signal acquired by a ground based microphone to an equivalent stationary signal. The benefit of the signal restoration is a simplification of the flight test requirements because it could dispense with the need to acquire acoustic data with another aircraft flying in concert with the rotorcraft. The data quality is also generally improved because the contamination of the signal by the propeller and wind noise is not present. The restoration methodology can also be combined with other data acquisition methods, such as a multiple linear microphone array for further improvement of the test results. The methodology and software are presented for performing the signal restoration in the time domain. The method has no restrictions on flight path geometry or flight regimes. Only requirement is that the aircraft spatial position be known relative to the microphone location and synchronized with the acoustic data. The restoration process assumes that the moving source radiates a stationary signal, which is then transformed into a nonstationary signal by various modulation processes. The restoration contains only the modulation due to the source motion.

Acoustic holography for wideband, arbitrarily shaped noise sources

Abstract: Acoustic holography has been shown to be a powerful technique for the study of sound radiation from complex structures. In its most rudimentary form, acoustic holography involves the measurement of a single frequency of sound throughout a spatial surface that corresponds to the level surface of a separable coordinate system. Most holography systems are limited to this basic form because of data acquisition and processing limitations. However, a high‐speed microphone array data acquisition system with an on‐line array processor and new data processing algorithms that permit acoustic holographic reconstructions of wideband noise sources with arbitrarily shaped surfaces has been developed. The data acquisition system is now described in detail in the literature. [Maynard et al., J. Acoust. Soc. Am. 78, 1395–1413 (1985); W. A. Veronesi and J. D. Maynard, J. Acoust. Soc. Am. 81, 1307–1322 (1987)]. In this paper, holography for odd‐shaped surfaces, i.e., surfaces that do not coincide with level surfaces of sepa...

A Digital Phase Delay Compensation Beam-Forming Scheme for Ultrasonic Imaging

Abstract: This paper describes an efficient digital implementation scheme of the phase delay compensation beam-former (PBF) for acoustic imaging using arrays, which is based on direct quadrature demodulation through sampling for narrowband signals. The scheme eliminates the need for analog quadrature demodulators employed in conventional digital PBFs and enables the sampling frequency to be reduced lower than the Nyquist rate. The lower bound of sampling frequency, within which images can be reconstructed without unacceptable degradation, has been experimentally studied by Bmode imaging in air using a microphone array.