頭部伝達関数の空間領域特性モデリング

Tohoku University鈴木陽一課

Efficient Computation of Slepian Functions for Arbitrary Regions on the Sphere

In this paper, we develop a new method for the fast and memory-efficient computation of Slepian functions on the sphere. Slepian functions, which arise as the solution of the Slepian concentration problem on the sphere, have desirable properties for applications where measurements are only available within a spatially limited region on the sphere and/or a function is required to be analyzed over the spatially limited region. Slepian functions are currently not easily computed for large band-limits for an arbitrary spatial region due to high computational and large memory storage requirements. For the special case of a polar cap, the symmetry of the region enables the decomposition of the Slepian concentration problem into smaller subproblems and consequently the efficient computation of Slepian functions for large band-limits. By exploiting the efficient computation of Slepian functions for the polar cap region on the sphere, we develop a formulation, supported by a fast algorithm, for the approximate computation of Slepian functions for an arbitrary spatial region to enable the analysis of modern datasets that support large band-limits. For the proposed algorithm, we carry out accuracy analysis of the approximation, computational complexity analysis, and review of memory storage requirements. We illustrate, through numerical experiments, that the proposed method enables faster computation, and has smaller storage requirements, while allowing for sufficiently accurate computation of the Slepian functions.Alice P. Bates is supported by the Australian Research Council’s Discovery Projects funding scheme (Project no. DP150101011). Rodney A. Kennedy is supported by the Australian Research Council’s Discovery Projects funding scheme (Project no. DP170101897)

Efficient representation of head-related transfer functions in continuous space-frequency domains

Utilizing spherical harmonic (SH) domain has been established as the default method of obtaining continuity over space in head-related transfer functions (HRTFs). This paper concerns different variants of extending this solution by replacing SHs with four-dimensional (4D) continuous functional models in which frequency is imagined as another physical dimension. Recently developed hyperspherical harmonic (HSH) representation is compared with models defined in spherindrical coordinate system by merging SHs with one-dimensional basis functions. The efficiency of both approaches is evaluated based on the reproduction errors for individual HRTFs from HUTUBS database, including detailed analysis of its dependency on chosen orders of approximation in frequency and space. Employing continuous functional models defined in 4D coordinate systems allows HRTF magnitude spectra to be expressed as a small set of coefficients which can be decoded back into values at any direction and frequency. The best performance was noted for HSHs and SHs merged with reverse Fourier-Bessel series, with the former featuring better compression abilities, achieving slightly higher accuracy for low number of coefficients. The presented models can serve multiple purposes, such as interpolation, compression or parametrization for machine learning applications, and can be applied not only to HRTFs but also to other types of directivity functions, e.g. sound source directivity.Comment: 33 pages, 9 figures, preprint of published paper submitted for green open access to fulfill funding institution mandat

A set of equations for numerically calculating the interaural level difference in the horizontal plane

The variation of interaural level difference (ILD) with direction and frequency is particularly complex and convoluted. The purpose of this work was to determine a set of parametric equations that can be used to calculate ILDs continuously at any value of frequency and azimuth in the horizontal plane. They were derived by fitting equations to ILDs derived from the azimuthal-dependence data tabulated by Shaw and Vaillancourt [(1985). J. Acoust. Soc Am. 78, 1120–1123] and assuming left-right symmetry. The equations are shown to fit those data to an overall RMS error less than 0.5 dB

Construction of a linear ion trap and engineering controlled spin-motional interactions

This thesis outlines the design and construction of an experimental system for confining and manipulating 171Yb+ ions in a linear trap. The experimental system is used to demonstrate two complementary techniques relating to entangling gates in trapped ions. Firstly, phase-modulated pulse sequences are used to perform motion-mediated entangling gates in a manner that enables robustness to noise, parameter flexibility and the ability to generate entanglement in large ion registers. Secondly, phase- and amplitude-modulated pulse sequences with tuneable noise sensitivity are used to perform spectrally-resolved sensing of fluctuations in the motional frequency of trapped ions. Together, these techniques form a joint framework for the measurement and suppression of error in trapped ion entangling gates

Compression pour la communication interactive de contenus visuels

Interactive images and videos have received increasing attention due to the interesting features they provide. With these contents, users can navigate within the content and explore the scene from the viewpoint they desire. The characteristics of these media make their compression very challenging. On the one hand, the data is captured in high resolution (very large) to experience a real sense of immersion. On the other hand, the user requests a small portion of the content during navigation. This requires two characteristics: efficient compression of data by exploiting redundancies within the content (to lower the storage cost), and random access ability to extract part of the compressed stream requested by the user (to lower the transmission rate). Classical compression schemes can not handle random accessibility because they use a fixed pre-defined order of sources to capture redundancies.The purpose of this thesis is to provide new tools for interactive compression schemes of images. For that, as the first contribution, we propose an evaluation framework by which we can compare different image/video interactive compression schemes. Moreover, former theoretical studies show that random accessibility can be achieved using incremental codes with the same transmission cost as non-interactive schemes and with reasonable storage overhead. Our second contribution is to build a generic coding scheme that can deal with various interactive media. Using this generic coder, we then propose compression tools for 360-degree images and 3D model texture maps with random access ability to extract the requested part. We also propose new representations for these modalities. Finally, we study the effect of model selection on the compression rates of these interactive coders.Les images et vidéos interactives ont récemment vu croître leur popularité. En effet, avec ce type de contenu, les utilisateurs peuvent naviguer dans la scène et changer librement de point de vue. Les caractéristiques de ces supports posent de nouveaux défis pour la compression. D'une part, les données sont capturées en très haute résolution pour obtenir un réel sentiment d'immersion. D'autre part, seule une petite partie du contenu est visualisée par l'utilisateur lors de sa navigation. Cela induit deux caractéristiques : une compression efficace des données en exploitant les redondances au sein du contenu (pour réduire les coûts de stockage) et une compression avec accès aléatoire pour extraire la partie du flux compressé demandée par l'utilisateur (pour réduire le débit de transmission). Les schémas classiques de compression ne peuvent gérer de manière optimale l’accès aléatoire, car ils utilisent un ordre de traitement des données fixe et prédéfini qui ne peut s'adapter à la navigation de l'utilisateur.Le but de cette thèse est de fournir de nouveaux outils pour les schémas interactifs de compression d’images. Pour cela, comme première contribution, nous proposons un cadre d’évaluation permettant de comparer différents schémas interactifs de compression d'image / vidéo. En outre, des études théoriques antérieures ont montré que l’accès aléatoire peut être obtenu à l’aide de codes incrémentaux présentant le même coût de transmission que les schémas non interactifs au prix d'une faible augmentation du coût de stockage. Notre deuxième contribution consiste à créer un schéma de codage générique pouvant s'appliquer à divers supports interactifs. À l'aide de ce codeur générique, nous proposons ensuite des outils de compression pour deux modalités d'images interactives : les images omnidirectionnelles (360 degrés) et les cartes de texture de modèle 3D. Nous proposons également de nouvelles représentations de ces modalités. Enfin, nous étudions l’effet de la sélection du modèle sur les taux de compression de ces codeurs interactifs

Error bounds for digital communication over spatially modulated channels.

Also issued as a Ph.D. thesis in the Dept. of Electrical Engineering, 1968.Bibliography: p.91-93