483 research outputs found

    Band Limited Signals Observed Over Finite Spatial and Temporal Windows: An Upper Bound to Signal Degrees of Freedom

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    The study of degrees of freedom of signals observed within spatially diverse broadband multipath fields is an area of ongoing investigation and has a wide range of applications, including characterising broadband MIMO and cooperative networks. However, a fundamental question arises: given a size limitation on the observation region, what is the upper bound on the degrees of freedom of signals observed within a broadband multipath field over a finite time window? In order to address this question, we characterize the multipath field as a sum of a finite number of orthogonal waveforms or spatial modes. We show that (i) the "effective observation time" is independent of spatial modes and different from actual observation time, (ii) in wideband transmission regimes, the "effective bandwidth" is spatial mode dependent and varies from the given frequency bandwidth. These findings clearly indicate the strong coupling between space and time as well as space and frequency in spatially diverse wideband multipath fields. As a result, signal degrees of freedom does not agree with the well-established degrees of freedom result as a product of spatial degrees of freedom and time-frequency degrees of freedom. Instead, analogous to Shannon's communication model where signals are encoded in only one spatial mode, the available signal degrees of freedom in spatially diverse wideband multipath fields is the time-bandwidth product result extended from one spatial mode to finite modes. We also show that the degrees of freedom is affected by the acceptable signal to noise ratio (SNR) in each spatial mode.Comment: Submitted to IEEE Transactions on Signal Processin

    Modeling and analysis of secondary sources coupling for active sound field reduction in confined spaces

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    This article addresses the coupling of acoustic secondary sources in a confined space in a sound field reduction framework. By considering the coupling of sources in a rectangular enclosure, the set of coupled equations governing its acoustical behavior are solved. The model obtained in this way is used to analyze the behavior of multi-input multi-output (MIMO) active sound field control (ASC) systems, where the coupling of sources cannot be neglected. In particular, the article develops the analytical results to analyze the effect of coupling of an array of secondary sources on the sound pressure levels inside an enclosure, when an array of microphones is used to capture the acoustic characteristics of the enclosure. The results are supported by extensive numerical simulations showing how coupling of loudspeakers through acoustic modes of the enclosure will change the strength and hence the driving voltage signal applied to the secondary loudspeakers. The practical significance of this model is to provide a better insight on the performance of the sound reproduction/reduction systems in confined spaces when an array of loudspeakers and microphones are placed in a fraction of wavelength of the excitation signal to reduce/reproduce the sound field. This is of particular importance because the interaction of different sources affects their radiation impedance depending on the electromechanical properties of the loudspeakers

    Source localization in reverberation environment based on improved equivalent sound source near-field acoustic holography algorithm

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    The compressive-equivalent source method near-field acoustic holography (C-ESM) is disturbed by reverberation in the enclosed space such as room and cabin, which leads to large reconstruction error and disturbs the judgment of sound source position. In order to solve this problem, an improved C-ESM algorithm based on room impulse response (RIR) is proposed to filter out reverberation interference in this paper. Different from the original equivalent source method, the improved algorithm constructs the transfer function through the room impulse response to establish the relationship between the equivalent source and the sound pressure on any plane in space, and the sparse signal reconstruction method of the compressive sensing technology is used to obtain the strength of the equivalent source. Then the transfer function to any plane of space is established according to the free field Green’s function, to eliminate the interference of reverberation and improve the effect of sound source location. The accuracy and effectiveness of the improved method are verified by preliminary numerical simulation. And the results show that compared with the original algorithm, this method has obvious advantages in sound source localization in a reverberant field

    Literature review of Direct Field Acoustic Noise (DFAN) testing

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    This report gives a comprehensive review of the state of the art in Direct Field Acoustic Noise (DFAN) testing based on published literature and product data. This is supplemented by background theory and selected best practice from other related disciplines. The report also aims to perform ‘horizon scanning’, and several suggestions are made for possible areas of future research and development.DFAN is found to be a maturing technology that is a suitable choice for high intensity acoustic testing of space-launch payloads. It does, however, bring its own set of unique challenges that require addressing. These are grouped into seven areas for future development in the concluding chapter.The most pressing needs, in our opinion, are for improved strategies for control of low frequency modes and methods for experimental assessment of diffuse fields. Both exploit practices that have been proven in room acoustics applications. These research questions could be explored through a mixture of simulation and experimentation and findings here would inform industrial best practice

    Active Noise Control Over Space: A Wave Domain Approach

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    Noise control and cancellation over a spatial region is a fundamental problem in acoustic signal processing. In this paper, we utilize wave-domain adaptive algorithms to iteratively calculate the secondary source driving signals and to cancel the primary noise field over the control region. We propose wave-domain active noise control algorithms based on two minimization problems: first, minimizing the wave-domain residual signal coefficients, and second, minimizing the acoustic potential energy over the region, and derive the update equations with respect to two variables, the loudspeaker weights and wave-domain secondary source coefficients. Simulation results demonstrate the effectiveness of the proposed algorithms, more specifically the convergence speed and the noise cancellation performance in terms of the noise reduction level and acoustic potential energy reduction level over the entire spatial region.DP14010341

    Contextualizing musical organics: an ad-hoc organological classification approach

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    As a research field, NIME is characterised by a plethora of design approaches, hardware, and software technologies. Formed of an interdisciplinary research community with divergent end-goals, the diversity of aims, objectives, methods, and outcomes is striking. Ranging from expressive interfaces, to musicological concerns, novel sensor technologies, and artificial creativity, the research presented is heterogeneous, distinct, and original. The design of digital instruments is very different from the making of acoustic instruments, due to the bespoke traditions and production environments of the disciplines mentioned above, but notably also because of the heightened epistemic dimension inscribed in the materiality of digital systems. These new materialities are often hardware and software technologies manufactured for purposes other than music. Without having to support established traditions and relationships between the instrument maker and the performer or composer, new digital musical instruments often develop at the speed of the computer’s technical culture, as opposed to the slower evolution of more culturally engrained acoustic instrument design

    Fourth Aircraft Interior Noise Workshop

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    The fourth in a series of NASA/SAE Interior Noise Workshops was held on May 19 and 20, 1992. The theme of the workshop was new technology and applications for aircraft noise with emphasis on source noise prediction; cabin noise prediction; cabin noise control, including active and passive methods; and cabin interior noise procedures. This report is a compilation of the presentations made at the meeting which addressed the above issues
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