Cette thèse se concentre sur l'individualisation des HRTF pour la synthèse binaurale. Les systèmes permettant de mesurer des HRTF sont difficiles d'accès au grand public, ce qui pose un problème pour la démocratisation de l'audio binaurale de haute qualité. C'est pour cette raison que nous recherchons une méthode permettant de calculer les HRTF d'une personne qu'à partir de la connaissance de sa morphologie. Ces travaux de thèse avancent sur les investigations visant à avoir une technique de personnalisation de l'audio binaurale. La technique de personnalisation proposée part du principe qu'il existe un lien direct et systématique liant des paramètres de la morphologie d'un individu avec les indices spectraux de ses HRTF. Elle est basée sur la détermination d'une fonction qui prend en entrée des paramètres morphologiques et qui donne en sortie des paramètres de transformation à appliquer à un jeu de HRTF existant pour obtenir un jeu de HRTF personnalisé. Cette fonction est estimée à partir d'analyses statistiques faits sur une base de données contenant des modèles numériques des individus ainsi que leurs HRTF. Pour atteindre cet objectif, il faut construire dans un premier temps les données à partir desquelles nous allons estimer notre fonction de personnalisation. Ces travaux expliquent les systèmes que nous avons conçus pour mesurer les HRTF des individus ainsi que pour obtenir leur modèle numérique tridimensionnel. De plus, les protocoles de mesure associés à chaque système sont expliqués. Enfin, nous expliquons comment les données obtenues peuvent être exploitées pour développer un procédé de personnalisation des HRTF. / This thesis focuses on the HRTF individualization problem in the context of binaural synthesis for general applications. HRTF strongly depend on morphological features of a person and, in order to provide compelling auditory spaces, binaural synthesis requires the use of individualized HRTF. Measuring or calculating the HRTF of a listener are common but lengthy and costly methods that are not feasible for general public applications. That is the reason why we aim to develop an alternative technique to obtain customized HRTF. The technique proposed relies on estimating the spectral cues of the HRTF, corresponding to the colorations induced by pinna filtering, from a person's morphology. The spectral cues represent the most complex and individual part of HRTF. The work presented in this thesis is based on the existence of a direct and systematic link between the morphology of a person and the spectral cues of their HRTF. The goal is to start from individualization techniques of HRTF and make studies for better understanding the relationship between the morphology of a person and their HRTF. The ultimate goal is then to find a proper morphological matching personalization technique. The first step to achieve this goal is to build the measuring systems who will help us create the databases that we will use for our analyses. This thesis explains the two measuring systems that were created and the measuring protocols that were used to create two related databases containing the 3D models and the measured HRTFs of a collection of people. We then explain how these databases can be used to fit the HRTF individualization technique we have proposed.

The acoustic scattering properties of the human head and torso match well with those of simple geometric shapes. Consequently, analytical scattering models can be utilised to account for the sound localisation cues introduced by these features. The traditional use of such models assumes that the head surface is completely rigid in nature. This thesis is concerned with modelling and understanding the effect of terminal scalp hair (i.e., a non-rigid head surface) on the auditory localisation cues. The head is modelled as a sphere, and the acoustical characteristics of hair are modelled using a locally-reactive equivalent impedance parameter. This allows the scattering boundary to be defined on the inner rigid surface of the head. The boundary assumptions are validated experimentally, through impedance measurement at oblique incidence and analysis of the near-field scattering pattern of a uniformly covered sphere. The impedance properties of human hair are also discussed, including trends with variations in sample thickness, bulk density, and fibre diameter. A general solution for the scattering of sound by a sphere with an arbitrarily distributed, locally reactive surface impedance is then presented. From this, an analytical solution is derived for a surface boundary that is evenly divided into two uniformly distributed hemispheres. For this boundary condition, cross-coupling is shown to exist between incoming and scattered wave modes of equi-order when the degrees are non-equal and opposite in parity. The overall effect of impedance on the resultant scattering characteristics is discussed in detail, both for uniform and for hemispherically divided surface boundaries. Finally, the analytical formulation and the impedance characteristics of hair are collectively utilised to investigate the effect of hair on human auditory localisation cues. The hair is shown to produce asymmetric perturbations to both the monaural and binaural cues. These asymmetries may help to resolve localisation confusions between sound stimuli positioned in the front and rear hemi-fields. The cue changes in the azimuth plane are characterised by two predominant features and remain consistent regardless of the decomposition baseline (i.e., the inclusion of a pinna offset, neck, etc). Experimental comparisons using a synthetic hair material show a good agreement with simulated results.

Spatialization of audio in the vertical plane has historically been limited. Instead, sound designers have used basic DSP to create pseudo height effects to explain the positions of corresponding objects. In recent years, binaural synthesis has become more widespread following an increase in the use of software rendering methods. With these advancements, uncertainty seems to be present around best practices when combining sound design with binaural synthesis for vertical placement of audio cues in games. This thesis compares the vertical localization performance between head related transfer functions (HRTFs) and stereo interaural level difference (ILD), when sounds have been designed with basic DSP to have auditory spatial schema (ASC). A sort of embedment of positional information. It was found that there was no significant time difference between the conditions, while hitcount, the number of correct directions selected, displayed a significant difference in some of the comparisons.