1,720,997 research outputs found
Multi-channel Kalman filters for active noise control
Full text linkBy formulating the feed-forward broadband active noise control problem as a state estimation problem it is possible to achieve a faster rate of convergence than the filtered reference least mean squares algorithm and possibly also a better tracking performance. A multiple input/multiple output Kalman algorithm is derived to perform this state estimation. To make the algorithm more suitable for real-time applications, the Kalman filter is written in a fast array form and the secondary path state matrices are implemented in output normal form. The resulting filter implementation is tested in simulations and in real-time experiments. It was found that for a constant primary path the filter has a fast rate of convergence and is able to track changes in the frequency spectrum. For a forgetting factor equal to unity the system is robust but the filter is unable to track rapid changes in the primary path. A forgetting factor lower than 1 gives a significantly improved tracking performance but leads to a numerical instability for the fast array form of the algorithm. © 2013 Acoustical Society of America
A numerically stable, finite memory, fast array recursive least squares filter for broadband active noise control
Full text linkSummary For broadband active noise control applications with a rapidly changing primary path, it is desirable to find algorithms with a rapid convergence, a fast tracking performance, and a low computational cost. Recently, a promising algorithm has been presented, called the fast-array Kalman filter, which uses rotation matrices to calculate the filter parameters. However, when this algorithm is implemented, it can show unstable behavior because of finite precision error propagation. In this paper, a novel algorithm is presented, which exhibits the fast convergence and tracking properties and the linear calculation complexity of the fast-array Kalman filter but does not suffer from the mentioned numerical problems. This is accomplished by running two finite length growing memory recursive least squares filters in parallel and using a convex combination of the two filters when the control signal is calculated. A reset of the filter parameters with proper re-initialization is enforced periodically. The mixing parameters will be chosen in such a way that the total available information used for the calculation of the control signal will be approximately equal at every time instance. The performance of the filter is shown in numerical simulations and real-time lab experiments. The numerical experiments show that the algorithm performs better numerically than the fast-array sliding window recursive least squares filter, while achieving a comparable convergence rate and tracking performance. The real-time lab experiments confirm the behavior shown in the simulations. Copyright © 2015 John Wiley & Sons, Ltd
Real-time Beamforming and Sound Classification Parameter Generation in Public Environments
No full textUndesired, human behavior in public environments is an increasing issue in today’s society. The overload of security operators and law enforcement addresses the need for automatic detection of anomalous behavior. The EU-project ADABTS aims to facilitate the protection of EU citizens, property and infrastructure against threats of terrorism, crime and riots, by the automatic detection of abnormal human behaviour. At the Acoustics & Sonar department of TNO Defence and Safety, part of this problem is addressed by means of acoustical detection of anomalous events. The approach is based on ‘scanning’ public environments by applying beamforming on the outputs of an acoustical sensor array and applying classification algorithms for detecting specific sources. In this Master’s thesis, an initial step is taken with the development of a real-time beamforming system that delivers required sound parameters used in sound classification. A number of different beamforming methods have been considered, differing in performance and computational complexity. Conventional methods like Delay and Sum (DAS), possibly combined with the use of static, frequency-invariant windows, lack spatial resolution at especially lower frequencies and are unable of coping with multiple interfering sources. Other methods provide an improved performance on the cost of increased complexity. The method known as Minimum Variance Distortionless Response (MVDR) beamforming maintains a high spatial resolution at lower frequencies. Two main versions of this method are frequently used: a static (non-input-based) one and a dynamic (input-based) one. Static MVDR (SMVDR) is able to maintain performance at lower frequencies, but due to its static nature it does not add any extra value in multi-source environments. Dynamic MVDR (DMVDR), on the other hand, is partly capable of filtering away undesired coherent interferers and also has an improved spatial response in single-source environments. Its computational complexity, still, is an important bottleneck. The search for less intensive beamforming methods leads to a way of adaptive beamforming. Beamformers in which static beamforming and dynamic filtering are split in two different parts, are able to alleviate complexity. However, the need for adding extra elements to account for target-signal cancellation in multi-source environments destroys the computational advantages, making it unsuitable. The developed real-time application takes into account the intensive routines of DMVDR. Since the properties of the deployment platform are not known in advance, it is supplied with a mechanism for adapting to different and changing, available hardware resources such as available CPU-time, arithmetic units and memory. In this way it will always deliver the best possible solution, based on what the user is offering. Still, an extensive implementation process has led to a relatively fast execution of the algorithm. The system is supplied with a user interface for controlling a number of parameters and for obtaining the first visual effects. Furthermore, it is provided with a user-friendly mechanism for calibrating the system for each possible deployment environment.MSPElectrical Engineering, Mathematics and Computer Scienc
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Ultrasonic imaging in aberrating media. Simulation methods for the design of aberration correction schemes
No full textVariations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Ultrasonic imaging in aberrating media: simulation methods for the design of aberration correction schemes
No full textAppropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Ultrasonic imaging in aberrating media: simulation methods for the design of aberration correction schemes
Full text linkContains fulltext :
mmubn000001_221315322.pdf (Publisher’s version ) (Open Access)Promotores : P. van den Berg, C. Gielen en J. Thijssen152 p
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