Loudspeaker Layout Research Articles

Spatial audio reproduction over ad hoc loudspeaker array using near-field compensation in spherical harmonics domain

Spatial audio reproduction using the loudspeaker array introduces the curvature effect leading to a distorted listening experience when the listener is in the near field. In the near-field, the loudspeakers are approximated as point sources (spherical wave) and amplify the mode vectors. Further, the problem becomes more challenging for the irregular loudspeaker arrangement, which causes uneven energy distribution in the reproduction region. In this context, a near-field compensation is applied to the encoded ambisonics coefficients. An optimization problem is formulated, such as the loudspeaker gains encoded with spherical harmonics basis coefficients should match the target ambisonics coefficients. Further, the in-phase and quadrature components of the energy localization vector are imposed as the constraints to direct maximum energy in the reproduction region. The solution to the optimization problem is obtained using a derivative-free optimization solver. The performance of the proposed methods is evaluated for ITU-R recommended loudspeaker layouts using the technical and perceptual evaluation attributes.

Deep Learning-Based Acoustic Echo Cancellation for Surround Sound Systems

Surround sound systems that play back multi-channel audio signals through multiple loudspeakers can improve augmented reality, which has been widely used in many multimedia communication systems. It is common that a hand-free speech communication system suffers from the acoustic echo problem, and the echo needs to be canceled or suppressed completely. This paper proposes a deep learning-based acoustic echo cancellation (AEC) method to recover the desired near-end speech from the microphone signals in surround sound systems. The ambisonics technique was adopted to record the surround sound for reproduction. To achieve a better generalization capability against different loudspeaker layouts, the compressed complex spectra of the first-order ambisonic signals (B-format) were sent to the neural network as the input features directly instead of using the ambisonic decoded signals (D-format). Experimental results on both simulated and real acoustic environments showed the effectiveness of the proposed algorithm in surround AEC, and outperformed other competing methods in terms of the speech quality and the amount of echo reduction.

Velocity controlled sound field reproduction by non-uniformly spaced loudspeakers

One approach to the reproduction of a sound field is to ensure the reproduction of the acoustic pressure on the surface bounding the volume within which reproduction is sought. However, this approach suffers from technical limitations when the loudspeakers used for the reproduction of the surface acoustic pressures are unevenly spaced. It is shown in this paper that sound field reproduction with a spatially non-uniform loudspeaker arrangement can be considerably improved by changing the physical quantity to be controlled on the bounding surface from pressure to particle velocity. One of the main advantages of the velocity control method is the simplicity with which the inverse problem can be regularized, irrespective of the direction of arrival of the sound to be reproduced. In addition, the velocity controlled sound field shows better reproduction of the time averaged intensity flow in the reproduction region which in turn appears to be closely linked with better human perception of sound localization. Furthermore, the proposed method results in smoother “panning functions” that describe the variation of the source outputs as a function of the angle of incidence of the sound to be reproduced. The performance of the velocity matching method has been evaluated by comparison to the conventional pressure matching method and through simulations with several non-uniform loudspeaker layouts. The simulated results were also verified with experiments and subjective tests.

Sector-Based Parametric Sound Field Reproduction in the Spherical Harmonic Domain

This papers presents a parametric method for perceptual sound field recording and reproduction from a small-sized microphone array to arbitrary loudspeaker layouts. The applied parametric model has been found to be effective and well-correlated with perceptual attributes in the context of directional audio coding, and here it is generalized and extended to higher orders of spherical harmonic signals. Higher order recordings are used for estimation of the model parameters inside angular sectors that provide increased separation between simultaneous sources and reverberation. The perceptual synthesis according to the combined properties of these sector parameters is achieved with an adaptive least-squares mixing technique. Furthermore, considerations regarding practical microphone arrays are presented and a frequency-dependent scheme is proposed. A realization of the system is described for an existing spherical microphone array and for a target loudspeaker setup similar to NHK 22.2. It is demonstrated through listening tests that, compared to a reference scene, the perceived difference is greatly reduced with the proposed higher order analysis model. The results further indicate that, on the same task, the method outperforms linear reproduction with the same recordings available.

Timbral and spatial fidelity improvement in ambisonics

Ambisonics renders a sound field through different kinds of loudspeaker layouts, which leads to different listening perceptions. While some loudspeaker arrays reinforce timbral fidelity, some improve localization accuracy. A split-band decoding is proposed that aims to select and then mix the better reconstructed frequency components from different loudspeaker arrays, thereby achieving the improved quality. The spectral reconstruction errors caused by truncation, comb filtering, and low-pass filtering are illustrated. The proposed solution is described, along with the experimental results from the listening tests. The split-band decoding method is especially suitable for binaural rendering and can also be applied to conventional loudspeaker arrays.

Evaluation of different spatial windows for a multi-channel audio interpolation system

The adoption rate of multi-channel audio systems has dramatically increased in recent years. It is common to find 5.1- or 7.1-channel systems in typical home theaters. However, most users do not setup the satellite loudspeakers at the prescribed positions for aesthetic reasons or due to space constraints. Recently, we introduced a technique to optimize multi-channel contents for reproduction over non-ideal loudspeaker setups. Our proposal improves localization accuracy for sound sources reproduced by horizontal loudspeaker arrays. It can also be extended to handle full 3D contents, like those of the upcoming 22.2-channel standard. The proposed method works by applying a set of spatial windows centered at the loudspeaker positions and interpolating along the angles using the spherical harmonics. We now extend our previous results by evaluating the performance of six different spatial window functions. We consider the 5-channel distribution of ITU recommendation BS.775-2, as well as four variations that end-users are likely to deploy. Apparent sound source locations are estimated from the energy and velocity vectors at the sweet spot. Our study found that using the Slepian window with our proposal and a non-ideal loudspeaker layout leads to a reproduced sound field that is closer to that of the ideal configuration.

New 3D audio for ultra high definition digital TV; loudspeaker configuration and method for virtual elevation effect rendering

This paper suggests the next-generation audio system for ultra high definition digital TV in terms of loudspeaker layout and corresponding rendering method. First part introduces the listening test results of perceived audio quality with several loudspeaker arrangements in order to find the optimal configuration of loudspeakers for a next-generation multichannel sound system. The subjective evaluations focused on the loudspeaker configurations at the top layer were carried out with test materials by mixing in studio and from B-format recordings. The results show that the perceptual difference in the overall quality achieved with the new 10.2-channel vertical surround system with 3 top loudspeakers and the reference system was imperceptible. Second part presents the virtual elevation effect rendering algorithm which can give a listener an impression of virtual 10.2 channel speakers using the conventional 7.1 channel speaker system (ITU-R BS.775-2) placed in horizontal plane. The proposed virtual height speaker rendering method consists of a generic head-related transfer function (HRTF) and a mixing algorithm based on four loudspeakers. For subjective evaluation three kinds of playbacks were compared; Original 10.2 channel signals, proposed 7.1 channel signals, and down-mixed 7.1 channel signals.

Investigating physical parameters associated with listeners' perceived auditory depth

Recent 3D technologies allow viewers to perceive disparities in the depths of visual objects and to thus experience more realistic visual information. As for 3D auditory display, however, conventional loudspeaker layouts have not managed to manipulate perceived auditory depth in a sufficiently convincing way. Previously, we proposed a new method that utilizes a prototype electrostatic loudspeaker that is located above the listening position and generates auditory images similar to those of headphones. Using this phenomenon and amplitude-based panning, we were able to move auditory images along the line connecting the front loudspeaker and the listening position. In this study, we investigated physical factors that were idiosyncratic in electrostatic loudspeaker reproduction and that caused listeners to perceive sounds as being nearby. We both measured and simulated the loudspeaker-to-ear transfer functions using various types of loudspeakers at multiple locations, and extracted several physical parameters, including the InterAural Phase Difference (IAPD) and the InterAural Level Difference (IALD). The result revealed a new physical quantity that was associated with loudspeaker-listener distance: variance in phase response differentials. We conclude that the electrostatic loudspeaker produced relatively less variance in phase response differentials and allowed listeners to perceive near auditory images as if listening to headphones and to enjoy better integrated 3D content.

3D sound field rendering under non‐idealized loudspeaker arrangements

The approach to realise periphonic sound field reproduction based on spherical harmonics (multi‐pole theory) has already been well‐known as Ambisonics and Higher Order Ambisonics, respectively. 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 physical configuration. First of all that demand bounds the reproduction of sound sources to the upper area. Furthermore caused by these facts idealized regular layouts considering the 3 dimensions are impossible. Within this contribution we will show how the symmetries of the spherical harmonics can be used to obtain optimized decoding rules and to overcome insufficient irregular loudspeaker arrangements.

Reduction of sound localization error for surround sound system using enhanced constant power panning law

In this paper, we propose an enhanced constant power panning (CPP) law which reduces the sound localization error in pair-wise panning for multi-channel loudspeaker layouts. In conventional CPP law, the phantom sound direction is usually different from the panning angle, especially when two loudspeakers are spread out widely. To overcome this problem, we propose an enhanced CPP law using directional psychoacoustic criteria (DPC). Analysis results show that the proposed method makes the same phantom sound direction as the panning angle in the audible frequency range. In addition, its performance is verified by means of a subjective sound localization test using a real sound source.

Surround sound apparatus

A surround sound apparatus wherein a decoder decodes directionally encoded audio signals for reproduction via a loudspeaker layout over a listening area wherein the signals are decoded by a matrix. The coefficients of the decoding matrix are such that at a predetermined listening position, the reproduced velocity vector direction and the reproduced energy vector position directions are substantially equal to each other and substantially independent of frequency in a broad audio frequency range The gain coefficients of the decoding matrix are such that the reproduced velocity vector magnitude varies systematically with encoded sound direction at frequencies in the region of and above a predetermined middle audio frequency.

Notions of conventional stereo in ‘‘Interaural cross-correlation coefficients in stereo-reproduced sound fields’’ [J. Acoust. Soc. Am. 8 5, 780–786 (1989)

Characterizations of stereo systems in Tohyama and Suzuki [J. Acoust. Soc. Am. 85, 780–786 (1989)] appear to be largely limited to diagrams of loudspeaker layout, including one for a so-called conventional stereo. Because of this, many readers may be unaware that the conclusions drawn are not generally applicable without further qualification. Omission of signal-format characterizations could, in principle, require the exclusion of certain stereo systems. In particular, one four-channel system could be regarded as excluded because it overturns a conclusion of Tohyama and Suzuki. Further, one stereo system that uses a conventional two-loudspeaker layout, but uses particularly apt signal formats, also overturns a conclusion.

Decoders for feeding irregular loudspeaker arrays

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