1,721,040 research outputs found
Regularization Approaches for Synthesizing HRTF Directivity Patterns
No full textAs an alternative to traditional artificial heads, it is possible to synthesize individual head-related transfer functions (HRTFs) using a so-called virtual artificial head (VAH), consisting of a microphone array with an appropriate topology and filter coefficients optimized using a narrowband least squares cost function. The resulting spatial directivity pattern of such a VAH is known to be sensitive to small deviations of the assumed microphone characteristics, e.g., gain, phase and/or the positions of the microphones. In many beamformer design procedures, this sensitivity is reduced by imposing a white noise gain (WNG) constraint on the filter coefficients for a single desired look direction. In this paper, this constraint is shown to be inappropriate for regularizing the HRTF synthesis with multiple desired directions and three alternative different regularization approaches are proposed and evaluated. In the first approach, the measured deviations of the microphone characteristics are taken into account in the filter design. In the second approach, the filter coefficients are regularized using the mean WNG for all directions. The third approach additionally takes into account several frequency bins into both the optimization and the regularization. The different proposed regularization approaches are compared using analytic and measured transfer functions, including random deviations. Experimental results show that the approach using multiple frequency bands mimicking the spectral resolution of the human auditory system yields the best robustness among the considered regularization approaches
Evaluation of head-tracked binaural auralizations of speech signals generated with a virtual artificial head in anechoic and classroom environments
No full textIn order to realize binaural auralizations with head tracking, BRIRs of individual listeners are needed for different head orientations. In this contribution, a filter-and-sum beamformer, referred to as virtual artificial head (VAH), was used to synthesize the BRIRs. To this end, room impulse responses were first measured with a VAH, using a planar microphone array with 24 microphones, for one fixed orientation, in an anechoic and a reverberant room. Then, individual spectral weights for 185 orientations of the listener’s head were calculated with different parameter sets. Parameters included the number and the direction of the sources considered in the calculation of spectral weights as well as the required minimum mean white noise gain (WNGm). For both acoustical environments, the quality of the resulting synthesized BRIRs was assessed perceptually in head-tracked auralizations, in direct comparison to real loudspeaker playback in the room. Results showed that both rooms could be auralized with the VAH for speech signals in a perceptually convincing manner, by employing spectral weights calculated with 72 source directions from the horizontal plane. In addition, low resulting WNGm values should be avoided. Furthermore, in the dynamic binaural auralization with speech signals in this study, individual BRIRs seemed to offer no advantage over non-individual BRIRs, confirming previous results that were obtained with simulated BRIRs
Dynamic Binaural Rendering: The Advantage of Virtual Artificial Heads over Conventional Ones for Localization with Speech Signals
No full textAs an alternative to conventional artificial heads, a virtual artificial head (VAH), i.e., a microphone array-based filter-and-sum beamformer, can be used to create binaural renderings of spatial sound fields. In contrast to conventional artificial heads, a VAH enables one to individualize the binaural renderings and to incorporate head tracking. This can be achieved by applying complex-valued spectral weights—calculated using individual head related transfer functions (HRTFs) for each listener and for different head orientations—to the microphone signals of the VAH. In this study, these spectral weights were applied to measured room impulse responses in an anechoic room to synthesize individual binaural room impulse responses (BRIRs). In the first part of the paper, the results of localizing virtual sources generated with individually synthesized BRIRs and measured BRIRs using a conventional artificial head, for different head orientations, were assessed in comparison with real sources. Convincing localization performances could be achieved for virtual sources generated with both individually synthesized and measured non-individual BRIRs with respect to azimuth and externalization. In the second part of the paper, the results of localizing virtual sources were compared in two listening tests, with and without head tracking. The positive effect of head tracking on the virtual source localization performance confirmed a major advantage of the VAH over conventional artificial heads
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Smoothing individual head-related transfer functions in the frequency and spatial domains
No full textWhen re-synthesizing individual head related transfer functions (HRTFs) with a microphone array, smoothing HRTFs spectrally and/or spatially prior to the computation of appropriate microphone filters may improve the synthesis accuracy. In this study, the limits of the associated HRTF modifications, until which no perceptual degradations occur, are explored. First, complex spectral smoothing of HRTFs into constant relative bandwidths was considered. As a prerequisite to complex smoothing, the HRTF phase spectra were substituted by linear phases, either for the whole frequency range or above a certain cut-off frequency only. The results indicate that a broadband phase linearization of HRTFs can be perceived for certain directions/subjects and that the thresholds can be predicted by a simple model. HRTF phase spectra can be linearized above 1 kHz without being detectable. After substituting the original phase by a linear phase above 5 kHz, HRTFs may be smoothed complexly into constant relative bandwidths of 1/5 octave, without introducing noticeable artifacts. Second, spatially smoother HRTF directivity patterns were obtained by levelling out spatial notches. It turned out that spatial notches do not have to be retained if they are less than 29 dB below the maximum level in the directivity pattern. (C) 2014 Acoustical Society of America
Variations on the Author
Get PDF“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
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe 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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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