1,213 research outputs found
Towards the Perceptual Optimisation of Virtual Room Acoustics
In virtual reality, it is important that the user feels immersed, and that both the visual and listening experiences are pleasant and plausible. Whilst it is now possible to accurately model room acoustics using available scene geometry in real time, the perceptual attributes may not always be optimal. Previous research has examined high level control methods over attributes, yet have only been applied to algorithmic reverberators and not geometric types, which can model the acoustics of a virtual scene more accurately. The present thesis investigates methods of perceptual control over apparent source width and tonal colouration in virtual room acoustics, and is an important step towards and intelligent optimisation method for dynamically improving the listening experience.
A review of the psychoacoustic mechanisms of spatial impression and tonal colouration was performed. Consideration was given to the effects early of reflections on these two attributes so that they can be exploited. Existing artificial reverb methods, mainly algorithmic, wave-based and geometric types, were reviewed. It was found that a geometric type was the most suitable, and so a virtual acoustics program that gave access to each reflection and their meta-data was developed. The program would allow for perceptual control methods to exploit the reflection meta-data.
Experiments were performed to find novel, directional regions to sort and group reflections by how they contribute to an attribute. The first was a region of in the horizontal plane, where any reflection arriving within it will produce maximum perceived apparent source width (ASW). Another discovered two regions of and unacceptable colouration in front of and behind the listener. Any reflection arriving within these will produce unacceptable colouration. Level adjustment of reflections within either region should manipulate the corresponding attributes, forming the basis of the control methods.
An investigation was performed where the methods were applied to binaural room impulse responses generated by the custom program in two different virtual rooms at three source-receiver distances. An elicitation test was performed to find out what perceptual differences the control methods caused using speech, guitar and orchestral sources. It was found that the largest differences were in ASW, loudness, distance and phasiness. Further investigation into the effectiveness of the control methods found that level adjustment of lateral reflections was fairly effective for controlling the degree of ASW without affecting tonal colouration. They also found that level adjustment of front-back reflections can affect ASW, yet had little effect on colouration. The final experiment compared both methods, and also investigated their effect on source loudness and distance. Again it was found that level adjustment in both regions had a significant effect on ASW yet little effect on phasiness. It was also found that they significantly affected loudness and distance. Analysis found that the changes in ASW may be linked to changes in loudness and distance
Efficient Synthesis of Room Acoustics via Scattering Delay Networks
An acoustic reverberator consisting of a network of delay lines connected via
scattering junctions is proposed. All parameters of the reverberator are
derived from physical properties of the enclosure it simulates. It allows for
simulation of unequal and frequency-dependent wall absorption, as well as
directional sources and microphones. The reverberator renders the first-order
reflections exactly, while making progressively coarser approximations of
higher-order reflections. The rate of energy decay is close to that obtained
with the image method (IM) and consistent with the predictions of Sabine and
Eyring equations. The time evolution of the normalized echo density, which was
previously shown to be correlated with the perceived texture of reverberation,
is also close to that of IM. However, its computational complexity is one to
two orders of magnitude lower, comparable to the computational complexity of a
feedback delay network (FDN), and its memory requirements are negligible
High Frequency Reproduction in Binaural Ambisonic Rendering
Humans can localise sounds in all directions using three main auditory cues: the differences in time and level between signals arriving at the left and right eardrums (interaural time difference and interaural level difference, respectively), and the spectral characteristics of the signals due to reflections and diffractions off the body and ears. These auditory cues can be recorded for a position in space using the head-related transfer function (HRTF), and binaural synthesis at this position can then be achieved through convolution of a sound signal with the measured HRTF. However, reproducing soundfields with multiple sources, or at multiple locations, requires a highly dense set of HRTFs. Ambisonics is a spatial audio technology that decomposes a soundfield into a weighted set of directional functions, which can be utilised binaurally in order to spatialise audio at any direction using far fewer HRTFs. A limitation of low-order Ambisonic rendering is poor high frequency reproduction, which reduces the accuracy of the resulting binaural synthesis.
This thesis presents novel HRTF pre-processing techniques, such that when using the augmented HRTFs in the binaural Ambisonic rendering stage, the high frequency reproduction is a closer approximation of direct HRTF rendering. These techniques include Ambisonic Diffuse-Field Equalisation, to improve spectral reproduction over all directions; Ambisonic Directional Bias Equalisation, to further improve spectral reproduction toward a specific direction; and Ambisonic Interaural Level Difference Optimisation, to improve lateralisation and interaural level difference reproduction. Evaluation of the presented techniques compares binaural Ambisonic rendering to direct HRTF rendering numerically, using perceptually motivated spectral difference calculations, auditory cue estimations and localisation prediction models, and perceptually, using listening tests assessing similarity and plausibility. Results conclude that the individual pre-processing techniques produce modest improvements to the high frequency reproduction of binaural Ambisonic rendering, and that using multiple pre-processing techniques can produce cumulative, and statistically significant, improvements
A Computer Vision Inspired Automatic Acoustic Material Tagging System for Virtual Environments
This paper presents the ongoing work on an approach to material information retrieval in virtual environments (VEs). Our approach uses convolutional neural networks to classify materials by performing semantic segmentation on images captured in the VE. Class maps obtained are then re-projected onto the environment. We use transfer learning and fine-tune a pretrained segmentation model on images captured in our VEs. The geometry and semantic information can then be used to create mappings between objects in the VE and acoustic absorption coefficients. This can then be input for physically-based audio renderers, allowing a significant reduction in manual material tagging
Movements in Binaural Space: Issues in HRTF Interpolation and Reverberation, with applications to Computer Music
This thesis deals broadly with the topic of Binaural Audio. After reviewing the
literature, a reappraisal of the minimum-phase plus linear delay model for HRTF
representation and interpolation is offered. A rigorous analysis of threshold based
phase unwrapping is also performed. The results and conclusions drawn from these
analyses motivate the development of two novel methods for HRTF representation
and interpolation. Empirical data is used directly in a Phase Truncation method. A
Functional Model for phase is used in the second method based on the
psychoacoustical nature of Interaural Time Differences. Both methods are validated;
most significantly, both perform better than a minimum-phase method in subjective
testing.
The accurate, artefact-free dynamic source processing afforded by the above
methods is harnessed in a binaural reverberation model, based on an early reflection
image model and Feedback Delay Network diffuse field, with accurate interaural
coherence. In turn, these flexible environmental processing algorithms are used in
the development of a multi-channel binaural application, which allows the audition
of multi-channel setups in headphones. Both source and listener are dynamic in this
paradigm. A GUI is offered for intuitive use of the application.
HRTF processing is thus re-evaluated and updated after a review of accepted
practice. Novel solutions are presented and validated. Binaural reverberation is
recognised as a crucial tool for convincing artificial spatialisation, and is developed
on similar principles. Emphasis is placed on transparency of development practices,
with the aim of wider dissemination and uptake of binaural technology
Surround by Sound: A Review of Spatial Audio Recording and Reproduction
In this article, a systematic overview of various recording and reproduction techniques for spatial audio is presented. While binaural recording and rendering is designed to resemble the human two-ear auditory system and reproduce sounds specifically for a listener’s two ears, soundfield recording and reproduction using a large number of microphones and loudspeakers replicate an acoustic scene within a region. These two fundamentally different types of techniques are discussed in the paper. A recent popular area, multi-zone reproduction, is also briefly reviewed in the paper. The paper is concluded with a discussion of the current state of the field and open problemsThe authors acknowledge National Natural Science Foundation of China (NSFC) No.
61671380 and Australian Research Council Discovery Scheme DE 150100363
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