4 research outputs found

    A methodology for sound scene manipulation based on the ray space transform

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    In this paper we devise a methodology for analysing and subsequently manipulating a sound scene acquired by means of a uniform linear array of microphones. The array signal is transformed in the ray space, i.e. a domain where acoustic rays are points; here we extract the source position and orientation in space and its radiation pattern, while its signal is extracted by a near-field beamformer. These descriptors can be easily manipulated and provided to any parametric rendering system. Through simulations we have proven the capability of the proposed method to perform different manipulations

    Efficient Continuous Beam Steering for Planar Arrays of Differential Microphones

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    Performing continuous beam steering, from planar arrays of high-order differential microphones, is not trivial. The main problem is that shape-preserving beams can be steered only in a finite set of privileged directions, which depend on the position and the number of physical microphones. In this letter, we propose a simple and computationally inexpensive method for alleviating this problem using planar microphone arrays. Given two identical reference beams pointing in two different directions, we show how to build a beam of nearly constant shape, which can be continuously steered between such two directions. The proposed method, unlike the diffused steering approaches based on linear combinations of eigenbeams (spherical harmonics), is applicable to planar arrays also if we deal with beams characterized by high-order polar patterns. Using the coefficients of the Fourier series of the polar patterns, we also show how to find a tradeoff between shape invariance of the steered beam, and maximum angular displacement between the two reference beams. We show the effectiveness of the proposed method through the analysis of models based on first-, second-, and third-order differential microphones

    Flexural Vibration Measurement and Sound Radiation Estimate of Thin Structures with Multiple Cameras

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    This thesis presents a simulation and experimental study focussed on the measurement of flexural vibration and on the estimate of the sound radiation of distributed structures by optical means and in particular by using multiple, i.e. more than two, synchronous cameras. The study considers two model problems composed by a cantilever beam and a plate excited by a tonal force at the first three fundamental resonance frequencies of flexural vibrations. The study has therefore considered the measurement of the deflection shapes at these frequencies, which accurately approximates the first three flexural mode shapes. The study is organized in four parts. The first part introduces the state of the art about the topic and revises the theoretical principles concerning optical measurements. The second part presents a simplified optical model employed to simulate how the accuracy of the measurements of the first three flexural deflection shapes of the structures here considered varies with respect to: a) the distance of the cameras from the structure; b) the angle of aperture between pairs of cameras; c) the elevation angle formed by the optical axis of the camera and the plane of the structure; d) the resolution of the cameras and e) the number of cameras. The principal objective of the study was indeed to show how the accuracy of the measurements can be significantly increased by using multiple cameras. The third part of the study provided experimental results taken on a beam rig and camera setup assembled using off-the-shelf devices. The experimental study focussed on the first flexural deflection shape of a cantilever beam and confirmed the findings of the simulation studies. The simulations and experiments presented in this work, quantify and confirm that the use of multiple cameras allows good vibration measurement accuracy, even at low spatial camera resolutions. Since the frame-rate and cost of cameras is limited by the amount of data they can process in each time unit, these results suggest that multiple, relatively cheap, high-speed, low-spatial resolution cameras can be used to perform vibration measurements in practical applications. The fourth part of the study examines the sound radiation generated by vibrating structures. In particular, it is evaluated how the accuracy of the estimate of the sound radiation emitted by the reconstructed first three flexural deflection shapes of a plate varies with respect to: a) the distance of the cameras from the structure; b) the azimuthal angle between the cameras; c) the elevation angle of the cameras; d) the resolution of cameras and e) the number of cameras. The principal objective of this fourth part was to understand if the results obtained on the influence on the flexural vibration measurements of the parameters listed above, could be applied to the case study of the estimate of the sound radiation
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