Reconstructing the high-order far-field directivity of a sound source using microphone arrays of arbitrary geometry : Application to measurements of the 3D directivity of human voice

Abstract : The directivity of a sound source describes the angular dependency of its radiated sound field. Over the past two decades, numerous research projects have investigated the directivity of natural sound sources, particularly that of the human voice. Indeed, the latter can present complex patterns due to the geometric peculiarities of the face and body of the speaker. Most of these works are affected by some of the following limitations. Firstly the estimates may be restricted to horizontal and/or vertical planes failing to account for the inherently 3D nature of vocal radiation. Going beyond 2D planes has been attained by either scanning a surrounding sphere by moving an array of microphones around the speaker, or paving the sphere with a rather low number of microphones. Both options have major drawbacks. The former relies on the strong assumption that vocalisations are repeatable enough to ensure a reliable 3D reconstruction, while the latter requires the use of interpolation methods to enhance the resolution of the directivity function estimate.

In this doctoral project, a state-of-the-art acoustic imaging technique that was originally introduced for Near-field Acoustic Holography (NAH) purposes is used to reconstruct the far-field directivity of sound sources. The Helmholtz Equation Least-Squares (HELS) method is based on the identification of the coefficients of the spherical wave decomposition of the sound field measured around the source. The main purpose of this thesis is to demonstrate the ability of the HELS method to yield consistent reconstructions of the sound field around human speakers and singers using microphone arrays of arbitrary geometry composed of a high number of microphones.

• Efren Fernandez-Grande (Univ. Politech. Madrid, rapporteur)
• Gilles Chardon (CentraleSupelec, rapporteur)
• Claudia Fritz (Inst. d'Alembert, Paris)
• Quentin Leclère (LVA, Lyon)
• Christoph Pörschmann (TU Köln)
• Thomas Hélie (IRCAM, Paris)
• Jean-Hugh Thomas (LAUM, Le Mans)
• François Ollivier (Institut d'Alembert, Paris, directeur de thèse)
• Fabrice Silva (LMA, Marseille, co-directeur de thèse, invité)