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Editorial

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172 KiB

Open AccessEditorial

Guest Editors’ Note—Special Issue on Spatial Audio

by Woon-Seng Gan and Jung-Woo Choi

Appl. Sci. 2017, 7(8), 788; https://doi.org/10.3390/app7080788 - 3 Aug 2017

Viewed by 4040

Abstract

Three-dimensional (or spatial) audio is a growing research field that plays a key role in realizing immersive communication in many of today’s applications for teleconferencing, entertainment, gaming, navigation guidance, and virtual reality (VR)/augmented reality (AR).[...] Full article

(This article belongs to the Special Issue Spatial Audio)

Research

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5797 KiB

Open AccessFeature PaperArticle

Auditory Distance Control Using a Variable-Directivity Loudspeaker

by Florian Wendt, Franz Zotter, Matthias Frank and Robert Höldrich

Appl. Sci. 2017, 7(7), 666; https://doi.org/10.3390/app7070666 - 29 Jun 2017

Cited by 12 | Viewed by 4494 | Correction

Abstract

The directivity of a sound source in a room influences the D/R ratio and thus the auditory distance. This study proposes various third-order beampattern pattern designs for a precise control of the D/R ratio. A comprehensive experimental study is conducted to investigate the [...] Read more.

The directivity of a sound source in a room influences the D/R ratio and thus the auditory distance. This study proposes various third-order beampattern pattern designs for a precise control of the D/R ratio. A comprehensive experimental study is conducted to investigate the hereby achieved effect on the auditory distance. Our first experiment auralizes the directivity variations using a virtual directional sound source in a virtual room using playback by a 24-channel loudspeaker ring. The experiment moreover shows the influence of room, source-listener distance, signal, and additional single-channel reverberation on the auditory distance. We verify the practical applicability of all the proposed beampattern pattern designs in a second experiment using a variable-directivity sound source in a real room. Predictions of experimental results are made with high accuracy, using room acoustical measures that typically predict the apparent source width. Full article

(This article belongs to the Special Issue Spatial Audio)

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6912 KiB

Open AccessFeature PaperArticle

Solution Strategies for Linear Inverse Problems in Spatial Audio Signal Processing

by Mingsian R. Bai, Chun Chung, Po-Chen Wu, Yi-Hao Chiang and Chun-May Yang

Appl. Sci. 2017, 7(6), 582; https://doi.org/10.3390/app7060582 - 5 Jun 2017

Cited by 11 | Viewed by 4600

Abstract

The aim of this study was to compare algorithms for solving inverse problems generally encountered in spatial audio signal processing. Tikhonov regularization is typically utilized to solve overdetermined linear systems in which the regularization parameter is selected by the golden section search (GSS) [...] Read more.

The aim of this study was to compare algorithms for solving inverse problems generally encountered in spatial audio signal processing. Tikhonov regularization is typically utilized to solve overdetermined linear systems in which the regularization parameter is selected by the golden section search (GSS) algorithm. For underdetermined problems with sparse solutions, several iterative compressive sampling (CS) methods are suggested as alternatives to traditional convex optimization (CVX) methods that are computationally expensive. The focal underdetermined system solver (FOCUSS), the steepest descent (SD) method, Newton’s (NT) method, and the conjugate gradient (CG) method were developed to solve CS problems more efficiently in this study. These algorithms were compared in terms of problems, including source localization and separation, noise source identification, and analysis and synthesis of sound fields, by using a uniform linear array (ULA), a uniform circular array (UCA), and a random array. The derived results are discussed herein and guidelines for the application of these algorithms are summarized. Full article

(This article belongs to the Special Issue Spatial Audio)

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2652 KiB

Open AccessArticle

Low Frequency Interactive Auralization Based on a Plane Wave Expansion

by Diego Mauricio Murillo Gómez, Jeremy Astley and Filippo Maria Fazi

Appl. Sci. 2017, 7(6), 558; https://doi.org/10.3390/app7060558 - 27 May 2017

Cited by 7 | Viewed by 5050

Abstract

This paper addresses the problem of interactive auralization of enclosures based on a finite superposition of plane waves. For this, room acoustic simulations are performed using the Finite Element (FE) method. From the FE solution, a virtual microphone array is created and an [...] Read more.

This paper addresses the problem of interactive auralization of enclosures based on a finite superposition of plane waves. For this, room acoustic simulations are performed using the Finite Element (FE) method. From the FE solution, a virtual microphone array is created and an inverse method is implemented to estimate the complex amplitudes of the plane waves. The effects of Tikhonov regularization are also considered in the formulation of the inverse problem, which leads to a more efficient solution in terms of the energy used to reconstruct the acoustic field. Based on this sound field representation, translation and rotation operators are derived enabling the listener to move within the enclosure and listen to the changes in the acoustic field. An implementation of an auralization system based on the proposed methodology is presented. The results suggest that the plane wave expansion is a suitable approach to synthesize sound fields. Its advantage lies in the possibility that it offers to implement several sound reproduction techniques for auralization applications. Furthermore, features such as translation and rotation of the acoustic field make it convenient for interactive acoustic renderings. Full article

(This article belongs to the Special Issue Spatial Audio)

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3053 KiB

Open AccessArticle

Stereophonic Microphone Array for the Recording of the Direct Sound Field in a Reverberant Environment

by Jonathan Albert Gößwein, Julian Grosse and Steven Van de Par

Appl. Sci. 2017, 7(6), 541; https://doi.org/10.3390/app7060541 - 24 May 2017

Cited by 1 | Viewed by 5658

Abstract

State-of-the-art stereo recording techniques using two microphones have two main disadvantages: first, a limited reduction of the reverberation in the direct sound component, and second, compression or expansion of the angular position of sound sources. To address these disadvantages, the aim of this [...] Read more.

State-of-the-art stereo recording techniques using two microphones have two main disadvantages: first, a limited reduction of the reverberation in the direct sound component, and second, compression or expansion of the angular position of sound sources. To address these disadvantages, the aim of this study is the development of a true stereo recording microphone array that aims to record the direct and reverberant sound field separately. This array can be used within the recording and playback configuration developed in Grosse and van de Par, 2015. Instead of using only two microphones, the proposed method combines two logarithmically-spaced microphone arrays, whose directivity patterns are optimized with a superdirective beamforming algorithm. The optimization allows us to have a better control of the overall beam pattern and of interchannel level differences. A comparison between the newly-proposed system and existing microphone techniques shows a lower percentage of the recorded reverberance within the sound field. Full article

(This article belongs to the Special Issue Spatial Audio)

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Open AccessFeature PaperArticle

Late Reverberation Synthesis Using Filtered Velvet Noise

by Vesa Välimäki, Bo Holm-Rasmussen, Benoit Alary and Heidi-Maria Lehtonen

Appl. Sci. 2017, 7(5), 483; https://doi.org/10.3390/app7050483 - 6 May 2017

Cited by 29 | Viewed by 6881

Abstract

This paper discusses the modeling of the late part of a room impulse response by dividing it into short segments and approximating each one as a filtered random sequence. The filters and their associated gain account for the spectral shape and decay of [...] Read more.

This paper discusses the modeling of the late part of a room impulse response by dividing it into short segments and approximating each one as a filtered random sequence. The filters and their associated gain account for the spectral shape and decay of the overall response. The noise segments are realized with velvet noise, which is sparse pseudo-random noise. The proposed approach leads to a parametric representation and computationally efficient artificial reverberation, since convolution with velvet noise reduces to a multiplication-free sparse sum. Cascading of the differential coloration filters is proposed to further reduce the computational cost. A subjective test shows that the resulting approximation of the late reverberation often leads to a noticeable difference in comparison to the original impulse response, especially with transient sounds, but the difference is minor. The proposed method is very efficient in terms of real-time computational cost and memory storage. The proposed method will be useful for spatial audio applications. Full article

(This article belongs to the Special Issue Spatial Audio)

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5011 KiB

Open AccessFeature PaperArticle

Objective Evaluation Techniques for Pairwise Panning-Based Stereo Upmix Algorithms for Spatial Audio

by Martin Mieth and Udo Zölzer

Appl. Sci. 2017, 7(4), 374; https://doi.org/10.3390/app7040374 - 10 Apr 2017

Cited by 2 | Viewed by 4636

Abstract

Techniques for generating multichannel audio from stereo audio signals are supposed to enhance and extend the listening experience of the listener. To assess the quality of such upmix algorithms, subjective evaluations have been carried out. In this paper, we propose an objective evaluation [...] Read more.

Techniques for generating multichannel audio from stereo audio signals are supposed to enhance and extend the listening experience of the listener. To assess the quality of such upmix algorithms, subjective evaluations have been carried out. In this paper, we propose an objective evaluation test for stereo-to-multichannel upmix algorithms. Based on defined objective criteria and special test signals, an objective comparative evaluation is enabled in order to obtain a quantifiable measure for the quality of stereo-to-multichannel upmix algorithms. Therefore, the basic functional principle of the evaluation test is demonstrated, and it is illustrated how possible results can be visualized. In addition, the proposed issues are introduced for the optimization of upmix algorithms and also for the clarification and illustration of the impacts and influences of different modes and parameters. Full article

(This article belongs to the Special Issue Spatial Audio)

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3304 KiB

Open AccessArticle

The Reduction of Vertical Interchannel Crosstalk: The Analysis of Localisation Thresholds for Natural Sound Sources

by Rory Wallis and Hyunkook Lee

Appl. Sci. 2017, 7(3), 278; https://doi.org/10.3390/app7030278 - 14 Mar 2017

Cited by 13 | Viewed by 5709

Abstract

In subjective listening tests, natural sound sources were presented to subjects as vertically-oriented phantom images from two layers of loudspeakers, ‘height’ and ‘main’. Subjects were required to reduce the amplitude of the height layer until the position of the resultant sound source matched [...] Read more.

In subjective listening tests, natural sound sources were presented to subjects as vertically-oriented phantom images from two layers of loudspeakers, ‘height’ and ‘main’. Subjects were required to reduce the amplitude of the height layer until the position of the resultant sound source matched that of the same source presented from the main layer only (the localisation threshold). Delays of 0, 1 and 10 ms were applied to the height layer with respect to the main, with vertical stereophonic and quadraphonic conditions being tested. The results of the study showed that the localisation thresholds obtained were not significantly affected by sound source or presentation method. Instead, the only variable whose effect was significant was interchannel time difference (ICTD). For ICTD of 0 ms, the median threshold was −9.5 dB, which was significantly lower than the −7 dB found for both 1 and 10 ms. The results of the study have implications both for the recording of sound sources for three-dimensional (3D) audio reproduction formats and also for the rendering of 3D images. Full article

(This article belongs to the Special Issue Spatial Audio)

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2426 KiB

Open AccessArticle

A Measure Based on Beamforming Power for Evaluation of Sound Field Reproduction Performance

by Ji-Ho Chang and Cheol-Ho Jeong

Appl. Sci. 2017, 7(3), 249; https://doi.org/10.3390/app7030249 - 3 Mar 2017

Cited by 4 | Viewed by 3891

Abstract

This paper proposes a measure to evaluate sound field reproduction systems with an array of loudspeakers. The spatially-averaged squared error of the sound pressure between the desired and the reproduced field, namely the spatial error, has been widely used, which has considerable problems [...] Read more.

This paper proposes a measure to evaluate sound field reproduction systems with an array of loudspeakers. The spatially-averaged squared error of the sound pressure between the desired and the reproduced field, namely the spatial error, has been widely used, which has considerable problems in two conditions. First, in non-anechoic conditions, room reflections substantially deteriorate the spatial error, although these room reflections affect human localization to a lesser degree. Second, for 2.5-dimensional reproduction of spherical waves, the spatial error increases consistently due to the difference in the amplitude decay rate, whereas the degradation of human localization performance is limited. The measure proposed in this study is based on the beamforming powers of the desired and the reproduced fields. Simulation and experimental results show that the proposed measure is less sensitive to room reflections and the amplitude decay than the spatial error, which is likely to agree better with the human perception of source localization. Full article

(This article belongs to the Special Issue Spatial Audio)

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Review

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2430 KiB

Open AccessFeature PaperReview

Spatial Audio for Soundscape Design: Recording and Reproduction

by Joo Young Hong, Jianjun He, Bhan Lam, Rishabh Gupta and Woon-Seng Gan

Appl. Sci. 2017, 7(6), 627; https://doi.org/10.3390/app7060627 - 16 Jun 2017

Cited by 78 | Viewed by 18542

Abstract

With the advancement of spatial audio technologies, in both recording and reproduction, we are seeing more applications that incorporate 3D sound to create an immersive aural experience. Soundscape design and evaluation for urban planning can now tap into the extensive spatial audio tools [...] Read more.

With the advancement of spatial audio technologies, in both recording and reproduction, we are seeing more applications that incorporate 3D sound to create an immersive aural experience. Soundscape design and evaluation for urban planning can now tap into the extensive spatial audio tools for sound capture and 3D sound rendering over headphones and speaker arrays. In this paper, we outline a list of available state-of-the-art spatial audio recording techniques and devices, spatial audio physical and perceptual reproduction techniques, emerging spatial audio techniques for virtual and augmented reality, followed by a discussion on the degree of perceptual accuracy of recording and reproduction techniques in representing the acoustic environment. Full article

(This article belongs to the Special Issue Spatial Audio)

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1396 KiB

Open AccessReview

Surround by Sound: A Review of Spatial Audio Recording and Reproduction

by Wen Zhang, Parasanga N. Samarasinghe, Hanchi Chen and Thushara D. Abhayapala

Appl. Sci. 2017, 7(5), 532; https://doi.org/10.3390/app7050532 - 20 May 2017

Cited by 85 | Viewed by 19498

Abstract

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 [...] Read more.

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 problems. Full article

(This article belongs to the Special Issue Spatial Audio)

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