Ambisonics and Wavefield Synthesis are two ways of rendering 3D audio, which both aim at physically reconstructing the sound field. Though they derive from distinct theoretical fundamentals, they have already been shown as equivalent under given assumptions. This paper further discusses their relationship by introducing new results regarding the coding and rendering of finite distance and enclosed sources. An updated view of the current knowledge is first given. A unified analysis of sound pickup and reproduction by mean of concentric transducer arrays then provides an insight into the spatial encoding and decoding properties. While merging the analysis tools of both techniques and investigating them on a common ground, general compromises are highlighted in terms of spatial aliasing, error and noise amplification.

Further Investigations of High-Order Ambisonics and Wavefield Synthesis for Holophonic Sound Imaging

Higher Order Ambisonics have been increasingly investigated in the past years, and found promising as a rational, scalable and flexible way to encode, transmit and r ender 3D sound fields. Nevertheless, studies concer ning virtual source imaging or natural 3D sound encoding mainly focussed on the directional encoding of plane waves , and neglected the near field effect of finite distance sources though it's present in any ordinary sound f ield. This paper highlights that with near field, the inf inite bass-boost affecting ambisonic components makes the currently accepted format unviable. By introducing from the e ncoding stage a near field compensation of reproduc tion loudspeakers, a viable, modified ambisonic format i s defined, distance-coding filters are designed, an d higher order ambisonic recording and synthesis become practicable.

http://decoy.iki.fi/dsound/ambisonic/motherlode/source/AES23%2520NFC%2520HOA.pdf

Spatial Sound Encoding Including Near Field Effect: Introducing Distance Coding Filters and a Viable, New Ambisonic Format

A sound system for capturing and reproducing sounds produced by a plurality of sound sources. The system comprises a device for receiving sounds produced by the plurality of sound sources and converting the separately received sounds to a plurality of separate audio signals without mixing the audio signals. The system may further comprise a device for separately storing the plurality of separate audio signals on a recording medium without mixing the audio signals and a device for reading the stored audio signals from the recording medium. A sound system and method for modeling a sound field generated by a sound source and creating a sound event based on the modeled sound field is also disclosed. The system and method captures a sound field over an enclosing surface, models the sound field and enables reproduction of the modeled sound field.

System and method for integral transference of acoustical events

Navigation within a closed environment requires analysis of a variety of acoustic cues, a task that is well developed in many visually impaired individuals, and for which sighted individuals rely almost entirely on visual information. For blind people, the act of creating cognitive maps for spaces, such as home or office buildings, can be a long process, for which the individual may repeat various paths numerous times. While this action is typically performed by the individual on-site, it is of some interest to investigate at which point this task can be performed off-site, at the individual's discretion. In short, is it possible for an individual to learn an architectural environment without being physically present? If so, such a system could prove beneficial for navigation preparation in new and unknown environments. The main goal of the present research can therefore be summarized as investigating the possibilities of assisting blind individuals in learning a spatial environment configuration through the listening of audio events and their interactions with these events within a virtual reality experience. A comparison of two types of learning through auditory exploration has been performed: in situ real displacement and active navigation in a virtual architecture. The virtual navigation rendered only acoustic information. Results for two groups of five participants showed that interactive exploration of virtual acoustic room simulations can provide sufficient information for the construction of coherent spatial mental maps, although some variations were found between the two environments tested in the experiments. Furthermore, the mental representation of the virtually navigated environments preserved topological and metric properties, as was found through actual navigation.

/pdf/exploration-of-architectural-spaces-by-blind-people-using-bu7swrqtz2.pdf

Exploration of architectural spaces by blind people using auditory virtual reality for the construction of spatial knowledge

Binaural audio provides a listener with 3D sound sensation, allowing a rich perceptual experience of the scene. However, binaural recordings are scarcely available and require nontrivial expertise and equipment to obtain. We propose to convert common monaural audio into binaural audio by leveraging video. The key idea is that visual frames reveal significant spatial cues that, while explicitly lacking in the accompanying single-channel audio, are strongly linked to it. Our multi-modal approach recovers this link from unlabeled video. We devise a deep convolutional neural network that learns to decode the monaural (single-channel) soundtrack into its binaural counterpart by injecting visual information about object and scene configurations. We call the resulting output 2.5D visual sound---the visual stream helps "lift" the flat single channel audio into spatialized sound. In addition to sound generation, we show the self-supervised representation learned by our network benefits audio-visual source separation. Our video results: http://vision.cs.utexas.edu/projects/2.5D_visual_sound/

2.5D Visual Sound

A computationally efficient 3D real time rendering engine for binaural sound reproduction via headphones is presented Binaural sound reproduction requires to filter the virtual sound source signals with head related transfer functions (HRTFs) To improve humans localization capabilities head tracking as well as room simulation have to be incorporated This yields the problem of high-quality, time-varying interpolation between different HRTFs To overcome this problem a virtual ambisonic approach is used that results in a bank of time-invariant HRTF filter

/pdf/a-3d-ambisonic-based-binaural-sound-reproduction-system-3ko9jl0qm3.pdf

A 3D Ambisonic Based Binaural Sound Reproduction System

Convincing binaural sound reproduction via headphones requires filtering the virtual sound source signals with head related transfer functions (HRTFs). Furthermore, humans are able to improve their localization capabilities by small unconscious head movements. Therefore it is important to incorporate head-tracking. This yields the problem of high-quality, time-varying interpolation between different HRTFs. A further improvement of human localization accuracy can be done by considering room simulation yielding a huge amount of virtual sound sources. To increase the computational efficiency of the proposed system, a virtual ambisonic approach is used, that result in a bank of time-invariant HRTF filter independent of the number of sources to encode.

/pdf/3d-binaural-sound-reproduction-using-a-virtual-ambisonic-1h1pxfobmt.pdf

3D binaural sound reproduction using a virtual ambisonic approach

A method of computationally efficient 3D sound reproduction via headphones is presented using a virtual Ambisonic approach. Previous studies have shown that incorporating head tracking as well as room simulation is important to improve sound source localization capabilities. The simulation of virtual acoustic space requires to filter the stimuli with head related transfer functions (HRTFs). In time-varying systems this yields the problem of high quality interpolation between different HRTFs. The proposed model states that encoding signals into Ambisonic domain results in time-invariant HRTF filters. The proposed system is implemented on a usual notebook using Pure Data (PD), a graphically based open source real time computer music software.

/pdf/a-3d-real-time-rendering-engine-for-binaural-sound-4yzp1iusci.pdf

A 3d real time rendering engine for binaural sound reproduction

Ambisonics is a 3D audio surround rendering and representat ion approach based on spherical harmonics with loudspeaker independent transmission channels. Although it wa s developed in the seventies and the techniques are well known, there are disagreements how to normalize, store and e xchange Ambisonic data. This paper’s mission is to propose a standard for the Ambison ics community and it should be seen as an encouragement to use the proposed convention, in order to facilitate excha nge and communication. This standard is named ambiX (Ambi sonics exchangeable). For the case that mixed order or reduced Ambisonic signal set s are beneficial, the format includes a simple matrix - named "adaptor matrix". This matrix can be freely configured to re- order, complete, re-normalize, or embed the transmitted or stored audio channels to a default set of periphonic Ambison ic signals. It is advocated as extended format, because it enables new techniques to reduce the Ambisonic signal set ut ilizing prior knowledge about restricted surround geometr ies like hemispherical or circular. Providing a default periph onic decoder for all surround geometries ensures universal applicability, while inspection tools for the adaptor matr ix are advanced means for optimal decoding. IEM provides a small "proof of concept" implementation of to ols to write, read audio data and the adaptor matrix, as well tools to analyze the adaptor matrix graphically to select th e best decoder for given files.

/pdf/ambix-a-suggested-ambisonics-format-2sgguz4kct.pdf

Alois Sontacchi

Papers

A 3D Ambisonic Based Binaural Sound Reproduction System

3D binaural sound reproduction using a virtual ambisonic approach

A 3d real time rendering engine for binaural sound reproduction

Ambix - a suggested ambisonics format

Producing 3D Audio in Ambisonics