21,068 research outputs found
A Human Head Shaped Array of Microphones and Cameras for Automotive Applications
No full textNowadays, a growing interest in the recording and reproduction of spatial audio was observed. However, despite many microphone arrays were developed in the last years, there are still few solutions for Noise, Vibration and Harshness (NVH) applications at low frequency. In this paper, a new array of microphones and cameras is presented, for recording both acoustic and visual spatial information. It can be used for the spatial analysis and visualization of the sound field and to perform recordings that can be rendered in a virtual reality (VR) environment. The system was optimized for the low frequency range, as most of the available solutions have proved unsatisfactory for frequencies below 400 Hz. Moreover, the system is cost-effective if compared to other existing products designed for similar applications. The spatial performance of the array is evaluated in comparison with the current state of the art systems. Finally, a field application is presented. The new head shaped microphone array demonstrated its effectiveness for evaluating the performance of an automotive Active Noise Control (ANC) system
Spherical t-Design for Characterizing the Spatial Response of Microphone Arrays
No full textMicrophone arrays are usually employed for spatial audio recordings and analysis. This requires converting the raw signals of the capsules into a 3D audio format, e.g., a spherical harmonics expansion. For processing such conversion, namely beamforming, it is necessary to know the complex response of each microphone of the array for many Directions-of-Arrival of the sound waves. This information constitutes the spatial response and describes how the wave fronts are diffracted by the surface of the array. Beyond the experimental, numerical, or theoretical method employed to get the spatial response, the shape of the array and the number of capsules, the choice of the Directions-of-Arrival of the sound waves is always critical. On one side, to maximize the spatial information and so the performance, on the other side to reduce the number of directions, and so the measurement or calculation time. The paper analyzes the problem of choosing an optimal geometry for obtaining the spatial response of a microphone array. It will be shown that spherical design, or T-design, allows maximizing the spatial information with the minimum amount of testing directions. Numerical and theoretical methods have been employed for characterizing two microphone arrays, a spherical and a non-spherical one. In both cases, Ambisonics format for spatial audio has been employed
Spherical Wave Diffraction for Microphone Arrays Operating in Near Field
No full textMicrophone arrays for spatial audio recording and reproduction became very popular in the last decade, due to the spread of virtual and augmented reality for entertainment, remote work, and teleconferencing. Several systems have been distributed on the market, and most of them are made of a rigid sphere. In this way, it is possible to rely on the theoretical solution of the plane wave diffraction to get the beamforming filters. Such filters are employed for synthesizing virtual microphones of arbitrary directivity by combining the signals recorded by the real microphones. However, the plane wave assumption corresponds to a far field condition, in which the wave fronts are planar or with negligible curvature.As the sound sources, or reflections, are closer to the array, the wave fronts tend to become spherical, and the planar hypothesis cannot be accepted. In this paper, the diffraction of spherical waves over a rigid sphere is investigated through numerical simulations based on Finite Elements Method and experimental measurements. It will be shown that the spatial performance is significantly degraded when theoretical filters are employed in near field conditions, while numerically calculated filters can provide a reliable improvement for near field beamforming
Recording, Analysis and Playback of Spatial Sound Field using Novel Design Methods of Transducer Arrays
No full textNowadays, a growing interest in the recording and reproduction of spatial audio has been observed. With virtual and augmented reality technologies spreading fast thanks to entertainment and video game industries, also the professional opportunities in the field of engineering are evolving. However, despite many microphone arrays are reaching the market, most of them is not optimized for engineering or diagnostic use and remains mainly confined to voice and music recordings.
In this thesis, the design of two new systems for recording and analysing the spatial distribution of sound energy, employing arrays of transducers and cameras, is discussed. Both acoustic and visual spatial information is recorded and combined together to produce static and dynamic colour maps, with a specially designed software and employing Ambisonics and Spatial PCM Sampling (SPS), two common spatial audio formats, for signals processing.
The first solution consists in a microphone array made of 32 capsules and a circular array of eight cameras, optimized for low frequencies. The size of the array is designed accordingly to the frequency range of interest for automotive Noise, Vibration & Harshness (NVH) applications. The second system is an underwater probe with four hydrophones and a panoramic camera, with which it is possible to monitor the effects of underwater noise produced by human activities on marine species.
Finite Elements Method (FEM) simulations have been used to calculate the array response, thus deriving the filtering matrix and performing theoretical evaluation of the spatial performance. Field tests of the proposed solutions are presented in comparison with the current state-of-the-art equipment.
The faithful reproduction of the spatial sound field arouses equally interest. Hence, a method to playback panoramic video with spatial audio is presented, making use of Virtual Reality (VR) technology, spatial audio, individualized Head Related Transfer Functions (HRTFs) and personalized headphones equalization.
The work in its entirety presents a complete methodology for recording, analysing and reproducing the spatial information of soundscapes
Metrics for Evaluating the Spatial Accuracy of Microphone Arrays
No full textThe interest in 3D audio is constantly growing, thus leading to the appearance on the market of many microphone arrays for recording spatial audio, having a variety of sizes, number of channels and shapes, mostly spherical. Among the various characteristics that may have an influence on the quality of these systems, the presented work will deal with the spatial accuracy. The availability of robust methods for evaluating the spatial performance of the microphone arrays allows to compare the systems and to study the effect of different geometries, or beamforming algorithms. On one side, the design of new solutions can be optimized, on the other side a user can identify an optimal system depending on his needs. In this paper, two metrics for evaluating the spatial performance of microphone arrays are described, and two common formats for spatial audio are employed, Ambisonics and Spatial PCM Sampling (SPS). In the first part, the parameters Spatial Correlation and Level Difference are used for assessing the accuracy of the Ambisonics format, which is based on Spherical Harmonics functions. In the second part two classic metrics for loudspeakers, i.e., directivity factor and half power beam width, are employed for evaluating the accuracy of unidirectional virtual microphones, which constitute the base of the SPS
format. In the last section, four well-known spherical microphone arrays are analyzed and compared through the described metrics and spatial audio formats
The Forgotten Measurement: Sound Pressure and Particle Velocity
No full textIn this article we explain how it is possible to record sound
pressure and particle velocity together underwater, thanks to
an old theory developed in the seventies. Most studies made
in the past on the effect of environmental noise pollution and
on the sensitivity of marine species to underwater noise were,
in fact, substantially wrong: limits specified only for sound
pressure caused a systematic underestimation of the potential
impact of noise, strongly biasing results
Low Frequency Simulations for Ambisonics Auralization of a Car Sound System
No full textIn this paper, a technique is described for obtaining the High Order Ambisonics (HOA) Impulse Responses (IRs) of an automotive infotainment system, relying on Finite Elements Method (FEM) simulations performed in COMSOL Multiphysics. The resulting HOA IRs are employed for auralizing the car sound system, either inside an Ambisonics listening room with a loudspeaker rig or with binaural
rendering on a Head Mounted Display (HMD), benefiting from head-tracking and personalized Head Related Transfer Functions (HRTFs). This allows performing subjective tests before the prototype is built and preserving the auditory experience with a degree of realism unattainable with the static binaural approach. Measurements performed in a prototype vehicle with a spherical microphone array are compared to FEM simulations. A good agreement between numerical and experimental methods have been demonstrated
Transducer Distribution on Spherical Arrays for Ambisonics Recording and Playback
No full textMicrophone and loudspeaker arrays are nowadays more and more employed in several applications, such as automotive industry, entertainment, immersive teleconferencing, or remote assistance. The position of the transducers over the surface of the array has a great influence on the beamforming, and so on the spatial performance. In this paper, a recurring geometrical problem is discussed: choosing the optimal locations of transducers for spherical arrays, either microphones or loudspeakers.None of the existing systems is currently relying on a spherical design, or t-design, for the arrangement of the transducers on the sphere. It will be shown that such mathematically optimized geometry is an optimal solution for the design of spherical arrays. They are the only known geometries ensuring a lossless transformation back and forth between the two most common spatial audio format: Ambisonics, which makes use of spherical harmonics, and Spatial PCM Sampling, which relies on unidirectional, high directivity virtual microphones
Report on Meteorological Research March 1, 1935 (m-1)
No full textThe object of the report was to elucidate in detail the various features of the research program in meteorology being carried on at the Daniel Guggenheim Airship Institute in Akron, Ohio. Mr. L. J. Fangman, of the U.S. Weather Bureau, was collaborating with the author in carrying out work such as a study of autographic records of the various meteorological elements during frontal passages with a view to the possible prediction of the intensity of the accompanying disturbance as it may affect the operation of aircraft and a study of atmospheric gustiness with a view to finding the dependence between frequency end amplitude of velocity fluctuations and the vertical temperature and velocity gradients
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