Ce projet de recherche a été mené dans le cadre du groupe de recherche NECOTIS (Neurosciences Computationnelles et Traitement Intelligent du Signal). Ce groupe de recherche agit principalement dans le domaine du traitement de l’image et de l’audio grâce à des méthodes de traitement de signal bio-inspirées. Différentes applications ont été développées en reconnaissance de la parole, dans la séparation de sources sonores ou encore en reconnaissance d’images. Bien qu’ils existent depuis plus de quarante ans, les systèmes d’aide aux personnes atteintes de déficiences visuelles, que cela soit des prothèses visuelles (invasif) ou des système de substitution sensorielle (non invasif), n’ont pas percé dans le milieu du handicap. Il serait difficile d’imputer cet état de fait à des limitations technologiques : depuis les premières approches, les prothèses visuelles ou les systèmes de substitution sensorielle n’ont cessé de se perfectionner et de se diversifier. Toutefois, si la question de savoir comment transmettre le signal est bien documentée, la question de savoir quel signal transmettre a été plus rarement abordée. Différents systèmes ont été développés mais le plus impressionnant est le récit des utilisateurs de tels systèmes. Ainsi, il fait plaisir de lire que l’artiste Neil Harbisson, qui ne voit aucune couleur, explique comment une caméra attachée à se tête lui permet d’entendre des couleurs et ainsi de pouvoir peindre [Montandon, 2004]. Un autre exemple tout aussi impressionnant, la scientifique Wanda Díaz-Merced, qui travaille pour xSonify, explique comment elle analyse différentes données en les encodant de façon sonore [Feder, 2012]. C’est dans ce cadre que ce projet de substitution sensorielle de la vision vers l’audition a été développé. En effet, nous avons utilisé le traitement de signal bio-inspiré afin d’extraire différentes caractéristiques représentatives de la vision. De plus, nous avons essayé de générer un son agréable à l’oreille et représentatif de l’environnement dans lequel évolue la personne. Ce projet a donc davantage été axé sur la nature du signal transmis à la personne ayant des déficiences visuelles.

Three experiments investigated the ability and means by which Florida manatees determine sound source directionality. An eight-choice discrimination paradigm determined the sound localization abilities of two manatees within a 360° array of speakers. Five conditions were tested including a 3,000 and 200 ms, 95 dB, 0.2-24 kHz signal, a 3,000 ms, 80 dB, 18-24 kHz signal, a 3000 ms, 110 dB, 0.2-1.5 kHz signal and a 200 ms, 101 dB, 4 kHz tonal signal. A sixth condition attenuated the level of the 3,000 ms, 95 dB, 0.2-24 kHz signal in 3 dB increments until accuracy reached 75%. Subjects performed above the 12.5% chance level for all broadband frequencies and were able to localize over a large level range. Errors were typically located to either side of the signal source location when presented in the front 180° but were more dispersed when presented from the 135°, 180° and 225° locations. Front-to-back confusions were few and accuracy was greater when signals originated from the front 180°. Head/body related transfer functions determined how different frequencies were filtered by the manatees' head/torso to create frequency-specific interaural level differences (ILDs). Hydrophones were suspended next to each manatee ear and Fast Fourier transform (FFT) ratios compared received signals with and without the subject's presence. ILD magnitudes were derived for all frequencies, as well as specific 0.2-1.5, 0.2-5, and 18-30 kHz bands of frequencies. ILDs were found for all frequencies as a function of source location, although they were largest with frequencies above 18 kHz and when signals originated at 90° and 270°. Larger ILDs were found when the signals originated behind the subjects as compared to in front of them. Auditory evoked potential (AEP) techniques were used to map manatee sound conduction pathways in-water and in-air using 15 and 24 kHz carriers. All subjects produced AEPs at each position the transducer was placed, however specific sound conduction pathway(s) were not identified. AEP amplitudes were usually greater with the 24 kHz carrier, however patterns between carriers at identical body positions were highly variable between subjects.

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.

Este trabalho apresenta diversas propostas associadas ao uso ótimo de funções de transferência relativas à cabeça (HRTFs) em sistemas de reprodução acústica virtual por fones de ouvido. Estas propostas permitem personalizar a HRTF a indivíduos particulares, tomando como base uma combinação da modelagem estrutural e morfológica de HRTFs. Dentro do contexto da modelagem estrutural, o presente trabalho se concentrou no estudo da contribuição do pinna à HRTF. O pinna é a estrutura anatômica responsável pela percepção de elevação. Assim, o primeiro passo foi extrair um conjunto de funções de transferência relativas ao pinna (PRTFs) das HRTFs de uma base de dados. Para tanto, foram usadas diversas técnicas como análise preditiva linear para rastrear as ressonâncias, janelamento para eliminar a influência do torso, funções de autocorrelação e de atraso de grupo para salientar as antirressonâncias, e outros algoritmos para combinar ressonâncias e antirressonâncias em apenas uma magnitude espectral. Usando essa nova base de dados de PRTFs e parâmetros antropométricos propostos mais outros registrados na base de dados, um espaço vetorial correspondente à antropometria do pinna foi mapeado linearmente em um espaço vetorial correspondente às características espectrais da PRTF, calculando-se assim várias transformações lineares para estimação de novas PRTFs fora da base de dados. A estimação atingiu 66% de reconstrução no grupo de treino. O trabalho está orientado à exploração das características espectrais importantes na percepção de elevação, portanto, está limitado ao plano médio do hemisfério frontal, onde não existem diferenças interaurais significativas nem efeitos difrativos da cabeça. Finalmente é proposto um sistema de testes de localização de fonte sonora para validar o modelo. / This work presents several proposals associated with the optimal use of head-related transfer functions (HRTF) in virtual auditory spaces presented via headphones. These proposals lead to personalization of the HRTF to particular individuals, using a combination of the structural and morphological modeling techniques. In the context of structural modeling, this work focuses on modeling the contribution of the pinna to the HRTF. The pinna is the anatomical structure responsible for vertical sound localization. Thus, the first step was to extract a set of pinna-related transfer functions (PRTFs) from HRTFs published in a database. This was accomplished using several techniques like linear prediction analysis for tracking the resonances, windowing for eliminating the torso influence, autocorrelation and group delay functions for emphasizing the notches and other algorithms for combining resonances and notches in only one magnitude response. Using this novel database of PRTFs and a set of proposed anthropometric parameters plus some others registered in the database, a vector space corresponding to pinna anthropometry is linearly mapped into a vector space corresponding to spectral features of the PRTF, being calculated, in this way, several linear transformations for estimation of new PRTFs, outside the database. The estimation attains 66% of reconstruction in the training group. The work focuses on the exploration of spectral characteristics important for elevation perception, therefore, it is limited to the median plane where there are no meaningful interaural differences nor head diffraction effects. Finally, a system for sound localization tests is proposed in order to validate the model.

Este trabalho apresenta diversas propostas associadas ao uso ótimo de funções de transferência relativas à cabeça (HRTFs) em sistemas de reprodução acústica virtual por fones de ouvido. Estas propostas permitem personalizar a HRTF a indivíduos particulares, tomando como base uma combinação da modelagem estrutural e morfológica de HRTFs. Dentro do contexto da modelagem estrutural, o presente trabalho se concentrou no estudo da contribuição do pinna à HRTF. O pinna é a estrutura anatômica responsável pela percepção de elevação. Assim, o primeiro passo foi extrair um conjunto de funções de transferência relativas ao pinna (PRTFs) das HRTFs de uma base de dados. Para tanto, foram usadas diversas técnicas como análise preditiva linear para rastrear as ressonâncias, janelamento para eliminar a influência do torso, funções de autocorrelação e de atraso de grupo para salientar as antirressonâncias, e outros algoritmos para combinar ressonâncias e antirressonâncias em apenas uma magnitude espectral. Usando essa nova base de dados de PRTFs e parâmetros antropométricos propostos mais outros registrados na base de dados, um espaço vetorial correspondente à antropometria do pinna foi mapeado linearmente em um espaço vetorial correspondente às características espectrais da PRTF, calculando-se assim várias transformações lineares para estimação de novas PRTFs fora da base de dados. A estimação atingiu 66% de reconstrução no grupo de treino. O trabalho está orientado à exploração das características espectrais importantes na percepção de elevação, portanto, está limitado ao plano médio do hemisfério frontal, onde não existem diferenças interaurais significativas nem efeitos difrativos da cabeça. Finalmente é proposto um sistema de testes de localização de fonte sonora para validar o modelo. / This work presents several proposals associated with the optimal use of head-related transfer functions (HRTF) in virtual auditory spaces presented via headphones. These proposals lead to personalization of the HRTF to particular individuals, using a combination of the structural and morphological modeling techniques. In the context of structural modeling, this work focuses on modeling the contribution of the pinna to the HRTF. The pinna is the anatomical structure responsible for vertical sound localization. Thus, the first step was to extract a set of pinna-related transfer functions (PRTFs) from HRTFs published in a database. This was accomplished using several techniques like linear prediction analysis for tracking the resonances, windowing for eliminating the torso influence, autocorrelation and group delay functions for emphasizing the notches and other algorithms for combining resonances and notches in only one magnitude response. Using this novel database of PRTFs and a set of proposed anthropometric parameters plus some others registered in the database, a vector space corresponding to pinna anthropometry is linearly mapped into a vector space corresponding to spectral features of the PRTF, being calculated, in this way, several linear transformations for estimation of new PRTFs, outside the database. The estimation attains 66% of reconstruction in the training group. The work focuses on the exploration of spectral characteristics important for elevation perception, therefore, it is limited to the median plane where there are no meaningful interaural differences nor head diffraction effects. Finally, a system for sound localization tests is proposed in order to validate the model.

Virtual three-dimensional auditory displays (V3DADs) use digital signal processing to deliver sounds (typically through headphones) that seem to originate from specific external spatial locations. This set of studies investigates the delivery of V3DADs through bone-conduction transducers (BCTs) in addition to conventional headphones. Although previous research has shown that spatial separation can be induced through BCTs, some additional signal adjustments are required for optimization of V3DADs, due to the difference in hearing pathways. The present studies tested a bone-conduction adjustment function (BAF) derived from equal-loudness judgments on pure tones whose frequencies were spaced one critical band apart. Localization performance was assessed through conventional air-conduction headphones, BCTs with only transducer correction, and BCTs with a BAF. The results showed that in the elevation plane, the BAF was effective in restoring the spectral cues altered by the bone-conduction pathway. No evidence for increased percept variability or decreased lateralization in the bone-conduction conditions was found. These findings indicate that a V3DAD can be implemented on a BCT and that a BAF will improve performance, but that there is an apparent performance cost that cannot be addressed with BAFs measured using the methodology in the present studies.