Physically-based auralization : design, implementation, and evaluation

The aim of this research is to implement an auralization system that renders audible a 3D model of an acoustic environment. The design of such a system is an iterative process where successive evaluation of auralization quality is utilized to further refine the model and develop the rendering methods. The work can be divided into two parts corresponding to design and implementation of an auralization system and evaluation of the system employing objective and subjective criteria. The presented auralization method enables both static and dynamic rendering. In dynamic rendering positions and orientations of sound sources, surfaces, or a listener can change. These changes are allowed by modeling the direct sound and early reflections with the image-source method. In addition, the late reverberation is modeled with a time-invariant recursive digital filter structure. The core of the thesis deals with the processing of image sources for auralization. The sound signal emitted by each image source is processed with digital filters modeling such acoustic phenomena as sound source directivity, distance delay and attenuation, air and material absorption, and the characteristics of spatial hearing. The digital filter design and implementation of these filters are presented in detail. The traditional image-source method has also been extended to handle diffraction in addition to specular reflections. The evaluation of quality of the implemented auralization system was performed by comparing recorded and auralized soundtracks subjectively. The compared soundtracks were prepared by recording sound signals in a real room and by auralizing these signals with a 3D model of the room. The auralization quality was assessed with objective and subjective methods. The objective analysis was based on both traditional room acoustic criteria and on a simplified auditory model developed for this purpose. This new analysis method mimics the behavior of human cochlea. Therefore, with the developed method, impulse responses and sound signals can be visualized with similar time and frequency resolution as human hearing applies. The evaluation was completed subjectively by conducting listening tests. The utilized listening test methodology is explained and the final results are presented. The results show that the implemented auralization system provides plausible and natural sounding auralizations in rooms similar to the lecture room employed for evaluation.reviewe

Comparison of auditory, visual, and audio-visual navigation in a 3D space

Proceedings of the 9th International Conference on Auditory Display (ICAD), Boston, MA, July 7-9, 2003.A navigation test was carried out in a spatially immersive virtual environment. The test was a game-like experience where task of subjects was to find as many gates as possible while they navigated through a track guided by auditory and/or visual cues of the gates. The results are presented as a function of the number of found gates, searching times, and normalized path lengths. Audio-visual navigation was clearly the most efficient. Visual navigation was the second, and the auditory navigation the least efficient. Further analysis of travel paths indicate that auditory cue was utilized in the beginning to locate the next gate, and visual cue was the most important in the final approach to the gate

Extending SMIL with 3D audio

Proceedings of the 9th International Conference on Auditory Display (ICAD), Boston, MA, July 7-9, 2003.This paper describes how SMIL can be extended to support 3D audio in a similar fashion than AABIFS does it for MPEG-4. The SMIL 2D layout is extended with an extra dimension to support a 3D space. New audio elements are positioned in the 3D space, whilst a listener element defines a listening point. Similarly to AABIFS perceptual modeling approach, an environment element describes environmental parameters for audio elements. These extensions enable interactive 3D audio capabilities in SMIL. In addition, any XML based rendering language could be extended with 3D audio capabilities by using a similar approach

Near-field evaluation of reproducible speech sources

The spatial speech reproduction capabilities of a KEMAR mouth simulator, a loudspeaker, the piston on the sphere model, and a circular harmonic fitting are evaluated in the near-field. The speech directivity of 24 human subjects, both male and female, is measured using a semicircular microphone array with a radius of 36.5 cm in the horizontal plane. Impulse responses are captured for the two devices, and filters are generated for the two numerical models to emulate their directional effect on speech reproduction. The four repeatable speech sources are evaluated through comparison to the recorded human speech both objectively, through directivity pattern and spectral magnitude differences, and subjectively, through a listening test on perceived coloration. Results show that the repeatable sources perform relatively well under the metric of directivity, but irregularities in their directivity patterns introduce audible coloration for off-axis directions.Peer reviewe

Spherical Decomposition of Arbitrary Scattering Geometries for Virtual Acoustic Environments

A method is proposed to encode the acoustic scattering of objects for virtual acoustic applications through a multiple-input and multiple-output framework. The scattering is encoded as a matrix in the spherical harmonic domain, and can be re-used and manipulated (rotated, scaled and translated) to synthesize various sound scenes. The proposed method is applied and validated using Boundary Element Method simulations which shows accurate results between references and synthesis. The method is compatible with existing frameworks such as Ambisonics and image source methods.publishedVersionPeer reviewe

Transfer-Plausibility of Binaural Rendering with Different Real-World References

For the evaluation of virtual acoustics for mixed realities, we distinguish between the paradigms "authenticity", "plausibility" and "transfer-plausibility". In the case of authenticity, discrimination tasks between real sound sources and virtual renderings presented over headphones are performed, whereas in case of a plausibility experiment, listeners need to rely only on their expectation of a sound when listening to the rendering, without the presence of an explicit reference. In the case of transfer-plausibility, however, different real sources are active alongside virtual sources, potentially in different spatial locations, leading to a certain degree of comparability. This resembles the case of forthcoming augmented reality systems. Here, we show an experiment, which assesses the transfer-plausibility of rendered speech sources in a variable acoustic environment. We demonstrate the influence of the similarity between real and virtual source material and their spatial location on the transfer-plausibility of measurement-based headphone rendering.Non peer reviewe

An exploratory investigation of speech recognition thresholds in noise with auralisations of two reverberant rooms

Objective Speech-in-noise tests are widely used in hearing diagnostics but typically without reverberation, although reverberation is an inextricable part of everyday listening conditions. To support the development of more real-life-like test paradigms, the objective of this study was to explore how spatially reproduced reverberation affects speech recognition thresholds in normal-hearing and hearing-impaired listeners. Design Thresholds were measured with a Finnish speech-in-noise test without reverberation and with two test conditions with reverberation times of similar to 0.9 and 1.8 s. Reverberant conditions were produced with a multichannel auralisation technique not used before in this context. Study sample Thirty-four normal-hearing and 14 hearing-impaired listeners participated in this study. Five people were tested with and without hearing aids. Results No significant differences between test conditions were found for the normal-hearing listeners. Results for the hearing-impaired listeners indicated better performance for the 0.9 s reverberation time compared to the reference and the 1.8 s conditions. Benefit from hearing aid use varied between individuals; for one person, an advantage was observed only with reverberation. Conclusions Auralisations may offer information on speech recognition performance that is not obtained with a test without reverberation. However, more complex stimuli and/or higher signal-to-noise ratios should be used in the future.Peer reviewe

Perceived feasibility of computer-generated auralization in concert halls

Over the years auralization has become a useful tool for simulating and evaluating the listening experience in virtual environments. Psychoacoustic phenomena, embodied by the human hearing system, highly determine the accuracy of sound-field recreation that is required for seemingly feasible auralization. In this scenario, the main aim of this study is to assess the suitability of computer-generated room impulse responses when used for auralizing spaces. To this purpose, simulated and experimentally measured binaural room impulse responses (BRIRs) have been convolved with iconic musical excerpts for various representative seats within a medium-sized concert hall. Listening tests have been thereby conducted and their results will be shown, analyzed and discussedEn estos últimos años, la auralización se ha convertido en una herramienta útil para la simulación y evaluación de la experiencia del oyente en entornos virtuales. En este ámbito, son de especial importancia los aspectos psicológicos y perceptivos, derivados del funcionamiento del sistema auditivo y del cerebro humanos, que determinan la precisión que se requiere para una recreación aparentemente creíble del campo sonoro. En este contexto, el principal objetivo de este estudio es evaluar la validez de respuestas al impulso de la sala generadas por ordenador para su utilización en la auralización de espacios. Con este propósito, para algunas localidades representativas de una sala de conciertos de tamaño medio, se han convolucionado varias respuestas al impulso binaurales (BRIRs), simuladas y medidas experimentalmente, con fragmentos musicales conocidos. Con los datos obtenidos, se han llevado a cabo pruebas de audición, cuyos resultados se presentan, analizan y discuten en esta comunicació