Wave Field Synthesis: The Future of Spatial Audio

Wave Field Synthesis is a technique for spatial sound reproduction that overcomes the limitations of classical stereophonic techniques. A thorough analysis of acoustic wave propagation prinicples delivers the technical description in terms of loudspeaker array technology. Suitable signal processing methods convert the source signals into driving signals for each loudspeaker. The suitability of this concept has been demonstrated by a number of implemented systems with some ten to a few hundred of loudspeakers. 1.Introduction Conventional systems for the reproduction of spatial audio are mainly based on intensity panning techniques. They typically adjust the contributions from two different loudspeaker channels in such a way that their superposition produces the required intensity levels at the listener's ears. Consequently, the spatial reproduction quality is only guaranteed in the vicinity of the targeted listener position. To enlarge the preferable listening area, several nove...

2000

Author Nick Zacharov Title Perceptual Studies on Spatial Sound Reproduction Systems This study considers research on spatial sound perception in the context of multichannel and other spatial sound reproduction systems. Issues associated with multichannel level alignment are discussed. Additionally aspects relating to the quality of spatial sound reproduction associated with loudspeaker directivity and 3D sound algorithms are considered. Lastly, a study of spatial sound perception is unfolded. This thesis contributes to the understanding of level alignment techniques from both a subjective and objective standpoint in multichannel sound reproduction schemes. The aim of these subjective experiments was to obtain a database of subject responses for a level alignment task under a wide range of normal usage situations, accounting for different source locations, distances, directivities, sensitivities, bandwidths and absolute reproduction levels. The data was analysed and correlated with a set of objective metrics measured for each test condition. From this analysis it is possible to ascertain superior test signal/metric combinations for perceptually motivated level alignment. Results may be directly applied to automated level calibration systems. Tools for binaural real-time loudness measurement are introduced allowing for the assessment of directional loudness characteristics and multiple source loudness alignment within arbitrary reveberation spaces. The second set of experiments focuses on issues influencing the quality of spatial sound reproduction under different multichannel sound reproduction scenarios. Firstly, the influence of loudspeaker directivity is subjectively assessed in a discrete five channel multichannel scenario. A set of experiments are presented that assess the influence of directivity both in the frontal and surround loudspeakers under idealised listening conditions. A range of virtual home theater systems are reviewed and a benchmark experiment is presented that compares their performance with respect to a discrete five channel multichannel reproduction. Evaluations are performed in an idealised "standard listening room" and real room conditions. Relative performances of each system are discussed in terms of relative spatial and timbral degradation. Lastly, initial studies are presented into the multidimensional perceptual unfolding of spatially processed speech reproduced over headphones. This study provides the basis for further studies in this area in an attempt to unravel or "unfold" the perceptual dimensions associated with spatial sound reproduction.

The Journal of the Acoustical Society of America

This research is based on the Binaural rendering from Surround sound. As Binaural and Surround systems are becoming more accurate and able to give a fully-immersive perception of sound through headphones, the importance of understanding how these systems work is necessary to better use, develop, and implement Binaural in the everyday routine. Binaural, its history, features and limitations has been analysed. Surround systems, such as 5.1 and Ambisonics, have been analysed and compared for Binaural Rendering purposes. Ambisonics has shown that its versatility and 360 degrees spatial audio characteristics can be used to accurately render Binaural signals.

Audio Signal Processing for Next-Generation Multimedia Communication Systems, 2004

Conventional multichannel audio reproduction systems for entertainment or communication are not capable of immersing a large number of listeners in a well defined sound field. A novel technique for this purpose is the so-called wave field synthesis. It is based on the principles of wave physics and suitable for an implementation with current multichannel audio hard-and software components. A multiple number of fixed or moving sound sources from a real or virtual acoustic scene is reproduced in a listening area of arbitrary size. The listeners are not restricted in number, position, or activity and are not required to wear headphones. A successful implementation of wave field synthesis systems requires to address also spatial aliasing and the compensation of non-ideal properties of loudspeakers and of listening rooms.

Stereophonic spatial sound reproduction systems with two, five, or more channels are designed for a certain listener position and work well in its vicinity, the so called sweet spot. For listeners at other positions, the quality of the spatial reproduction may be degraded. This contribution describes an advanced spatial reproduction technique called wave field synthesis. It is based on a physical description of acoustic wave propagation and uses loudspeaker array technology for sound field reproduction without the sweet spot limitation. After discussing the physical foundations, the main steps from the acoustic description to the determination of the loudspeaker signals are outlined. Finally an implementation of a wave field synthesis system with 48 channels is presented.

HTTP://www.ambiophonics.org This paper discusses the psychoacoustical background and the computational issues involved in the real-time implementation of a complete Ambiophonics reproduction system based on binaural technology. Ambiophonics, which requires only two media channels, evolved from previously known approaches such as the reproduction of binaural recordings over closely spaced loudspeakers through cross-talk cancellation, and the reconstruction of hall ambience by convolution from suitable impulse responses. The equations for the design of the digital filter coefficients are derived with regard to the many possible kinds of pre-existing recordings (binaural, sphere, ORTF, M/S), and their implementation on available hardware and software platforms are described. The authors suggest psychoacoustic explanations for the perceived audible performance, and describe the first results of a comparative listening test, evaluating the realism of three periphonic surround reproduction systems: Stereo Dipole, Ambisonics and Ambiophonics.

2014

In contrast to two other multichannel sound-field synthesis techniques, Higher Order Ambisonics (HOA) and Wavefield Synthesis (WFS), Discrete Multichannel Simulation (DMS) has distinct advantages in the display of three-dimensional virtual acoustic sound fields for human listeners. In particular, it is the impact of listener head movements on reproduction fidelity that is the primary concern, although the influence of static head acoustics on the displayed sound field is another critical factor. Whereas movement of the listener's head outside of the 'sweet spot' for HOA can result in dramatic failure in terms of both spatial and timbral performance of a sound-field display system, given a large number of loudspeakers, a value of the DMS system is that the configuration of simulated sources and reflections is fixed on each of the respective loudspeakers even though the absolute angles vary with head translation and rotation. Experiences in the design and evaluation of thr...

The Journal of the Acoustical Society of America, 2008

The approach to realise periphonic sound field reproduction based on spherical base solutions of the wave equation has already been well-known as Ambisonics and High Order Ambisonics (HOA), respectively (see ). By the aid of an N-dimensional orthogonal set of vectors any arbitrary source free sound field can be described. Reproduction is realized by projection of the encoded sound field on a regular loudspeaker distribution over a spherical surface. The used set of vectors exhibits a defined hierarchic with interesting symmetries. In the original scheme sound sources represented by plane waves (sources in far distance) can be encoded independent of the decoding process on the regular loudspeaker layout. Usually, in practice -in contrast to theory, 3D loudspeaker layouts are requested for the upper hemisphere. This restriction is caused by the geometry of many rooms. First of all that restriction bounds the reproduction of sound sources to the upper area. With a complete set of N-th order spherical harmonics in such discussed cases a regular design of a HOA decoder is impossible.

2003

Holophonic sound reproduction using Wave Field Synthesis (WFS) (1) aims at recreating a virtual spatialized sound scene in a n ex- tended area. Applying this technique to synthesize virtual sources located within an indoor environment can create striking audio ef- fects in the context of virtual or augmented reality applica tions. However, interactions of the synthesized sound field with th e lis- tening room must be taken into account for they cause modifica - tions in the resulting sound field. This paper enumerates som e of these interactions according to different virtual scene co nfigura- tions and applications. Particular attention is paid to the repro- duction of the sound source directivity and to the reproduction of a room effect coherent with the real environment. Solutions for synthesizing the directivity of the source and the associat ed room effect are proposed and discussed around simulations, developpe- ments and first perceptual validation. 1. CONTEXT

Wave field synthesis and Ambisonics strive to reconstruct a sound field within a listening area using the interference of loudspeaker signals. Due to the spatial sampling, an error-free reconstruction is not achieved within the entire listening area and consequently, the perceived quality of the reproduction may be impaired. Specifically, sound events may be localized incorrectly and the individual loudspeaker signals may result in perceived coloration. Here, a binaural auditory model was employed to predict the localization error in several off-center-listening positions and to visualize coloration artifacts. The model outputs provided good match for perceptual data from previously conducted listening tests, verifying the applicability of the model to evaluate the reconstructed sound fields.

Journal of Sound and Vibration, 1997

2007

The paper describes the sound systems and the listening rooms installed in the new "museum of reproduced sound", actually being built in Parma, restoring an ancient church. The museum is devoted to the exposition of a huge collection of antique radios and gramophones, but it will also exploit the frontiers of modern methods for immersive surround reproduction: WFS and HOA. In the main hall, a large planar WFS loudspeaker array is employed for inviting the visitors to enter the world of sound reproduction, providing stunning effects and emotional sounds enveloping them from many directions. At the end of the exposition path, a special HOA space is employed for showing the recent developments of recording/reproduction methods started from the Ambisonics concept, capable of creating natural reproduction of sport events, live music and other immersive acoustical experiences; in this room also a binaural/transaural system is available. A second, larger listening room capable of...

2000

The antique stereophonic recording and playback format is going to be replaced by new surround sound formats in the near future. At the moment, various surround techniques are being investigated in many artistic and technical applications. The main concern is to find an appropriate recording and playback format which supports the natural spatial hearing cues. Therefore, surround sound systems should provide a homogeneous and coherent sound field image, both for recorded and synthesized sound fields [1]. In a homogeneous sound reproduction system, no direction is treated preferentially. Coherent sound field image means that the image remains stable under changes of the listener position, though the image may change as a natural sound field does. The Holophony and Ambisonic system described by Nicol and Emerit [2] is the basic approach. This system will be extended by a new approach to compensate the interfering reflections of the reproduction room. Further possibilities to determine higher order Ambisonic signals using the beam forming approach are investigated.

2015

This contribution reviews the basics of Ambisonics and outlines examples of applied Ambisonics using microphone and loudspeaker arrays, and headphone-based rendering. Recent achievements will be addressed in Ambisonic software, panning and decoding, and the observation and optimizing of perceptual properties. Moreover, another highly topical field of higher-order Ambisonic recording is discussed, its fundamental spatial resolution versus SNR and bandwidth problem, a new filtering approach, and spatial mastering effects.