Vector Base Amplitude Panning Research Articles

Sound field synthesis for psychoacoustic research: In situ evaluation of auralized sound pressure levela).

The use of virtual acoustic environments has become a key element in psychoacoustic and audiologic research, as loudspeaker-based reproduction offers many advantages over headphones. However, sound field synthesis methods have mostly been evaluated numerically or perceptually in the center, yielding little insight into the achievable accuracy of the reproduced sound field over a wider reproduction area with loudspeakers in a physical, laboratory-standard reproduction setup. Deviations from the ideal free-field and point-source concepts, such as non-ideal frequency response, non-omnidirectional directivity, acoustic reflections, and diffraction on the necessary hardware, impact the generated sound field. We evaluate reproduction accuracy in a 61-loudspeaker setup, the Simulated Open Field Environment, installed in an anechoic chamber. A first measurement following the ISO 8253-2:2009 standard for free-field audiology shows that the required accuracy is reached with critical-band-wide noise. A second measurement characterizes the sound pressure reproduced with the higher-order Ambisonics basic decoder, with and without max rE weighting, vector base amplitude panning, and nearest loudspeaker mapping on a 187 cm × 187 cm reproduction area. We show that the sweet-spot size observed in measured sound fields follows the rule kr≤N/2 rather than kr≤N but is still large enough to avoid compromising psychoacoustic experiments.

The impact of head-related impulse response delay treatment strategy on psychoacoustic cue reconstruction errors from virtual loudspeaker arrays.

Known errors exist in loudspeaker array processing techniques, often degrading source localization and timbre. The goal of the present study was to use virtual loudspeaker arrays to investigate how treatment of the interaural time delay (ITD) cue from each loudspeaker impacts these errors. Virtual loudspeaker arrays rendered over headphones using head-related impulse responses (HRIRs) allow flexible control of array size. Here, three HRIR delay treatment strategies were evaluated using minimum-phase loudspeaker HRIRs: reapplying the original HRIR delays, applying the relative ITD to the contralateral ear, or separately applying the HRIR delays prior to virtual array processing. Seven array sizes were simulated, and panning techniques were used to estimate HRIRs from 3000 directions using higher-order Ambisonics, vector-base amplitude panning, and the closest loudspeaker technique. Compared to a traditional, physical array, the prior HRIR delay treatment strategy produced similar errors with a 95% reduction in the required array size. When compared to direct spherical harmonic (SH) fitting of head-related transfer functions (HRTFs), the prior delays strategy reduced errors in reconstruction accuracy of timbral and directional psychoacoustic cues. This result suggests that delay optimization can greatly reduce the number of virtual loudspeakers required for accurate rendering of acoustic scenes without SH-based HRTF representation.

3-D Sound Image Reproduction Method Based on Spherical Harmonic Expansion for 22.2 Multichannel Audio

In this paper, we propose a three-dimensional (3-D) sound image reproduction method based on spherical harmonic (SH) expansion for 22.2 multichannel audio. 22.2 multichannel audio is a 3-D sound field reproduction system that has been developed for ultra-high definition television (UHDTV). This system can reproduce 3-D sound images by simultaneously driving 22 loudspeakers and two sub-woofers. To control the 3-D sound image, vector base amplitude panning (VBAP) is conventionally used. VBAP can control the direction of 3-D sound image by weighting the input signal and emitting it from three loudspeakers. However, VBAP cannot control the distance of the 3-D sound image because it calculates the weight by only considering the image’s direction. To solve this problem, we propose a novel 3-D sound image reconstruction method based on SH expansion. The proposed method can control both the direction and distance of the 3-D sound image by controlling the sound directivity on the basis of spherical harmonics (SHs) and mode matching. The directivity of the 3-D sound image is obtained in the SH domain. In addition, the distance of the 3-D sound image is represented by the mode strength. The signal obtained by the proposed method is then emitted from loudspeakers and the 3-D sound image can be reproduced accurately with consideration of not only the direction but also the distance. A number of experimental results show that the proposed method can control both the direction and distance of 3-D sound images.

Improved accuracy and computational efficiency in virtual acoustic rendering using principal components-based amplitude panning

Virtual loudspeaker arrays can be rendered over headphones using a head-related impulse response (HRIR) dataset, but these techniques often introduce undesirable spatial and timbral artifacts that are associated with distortions in the interaural level difference (ILD) cue. Here, a new and efficient virtual acoustic rendering technique that minimizes ILD distortions is described and evaluated. The technique uses principal components analysis (PCA) performed on the time-domain minimum-phase representation of the directionally dependent HRIRs. The resulting principal components (PCs) act as virtual acoustic filters, and the PCA scores are implemented as panning gains. These panning gains map the PC filters to source locations, similar to vector-base amplitude panning (VBAP). Thus, the technique is termed principal components-based amplitude panning (PCBAP). A spatial and spectral error analysis of ILD shows similar reconstruction accuracy is obtained using PCBAP with 15 filters compared to a 256-loudspeaker VBAP array. PCBAP is also scalable to simulate large loudspeaker arrays with a fixed set of PC filters and only small increases in computational requirements. Results from psychophysical testing suggest that perceptual equivalence between a PCBAP-rendered source and a reference source rendered with the original HRIR dataset is directionally dependent but can be achieved with as few as 10–20 PCs.

Comparison of 3D Audio Reproduction Methods Using Hearing Devices

In order to study 3D auditory perception for hearing aid users, spatial audio reproduction systems have been considered. Numerous solutions were designed in the past, but few studies evaluated the effect of 3D audio reproduction artifacts on hearing devices. This study focuses on loudspeaker-based 3D audio reproduction and compares the effects of distance-based amplitude panning (DBAP), third and fifth order Ambisonics (HOA), multiple-direction amplitude panning (MDAP), and vector-base amplitude panning (VBAP) on the 3D directivity index (DI) of hearing device beamformers, on interaural time differences (ITD), and on interaural level differences (ILD). Measurements were conducted at the sweet spot and for two off-center positions in a non-anechoic room using 32 loudspeakers. Results show that the effect of the reproduction system on the DI at the sweet spot was larger for third order Ambisonics and MDAP and smaller for fifth order Ambisonics. They also show that DBAP cannot reproduce ITDs correctly and that the ILDs obtained with HOA reproduction contain larger errors than with the other reproduction systems. Finally the results show that the DI, ITD, and ILD errors increase with the distance to the sweet spot and that this increase is larger for HOA than for the other reproduction methods

Spatial Resolution of Late Reverberation in Virtual Acoustic Environments.

Late reverberation involves the superposition of many sound reflections, approaching the properties of a diffuse sound field. Since the spatially resolved perception of individual late reflections is impossible, simplifications can potentially be made for modelling late reverberation in room acoustics simulations with reduced spatial resolution. Such simplifications are desired for interactive, real-time virtual acoustic environments with applications in hearing research and for the evaluation of hearing supportive devices. In this context, the number and spatial arrangement of loudspeakers used for playback additionally affect spatial resolution. The current study assessed the minimum number of spatially evenly distributed virtual late reverberation sources required to perceptually approximate spatially highly resolved isotropic and anisotropic late reverberation and to technically approximate a spherically isotropic sound field. The spatial resolution of the rendering was systematically reduced by using subsets of the loudspeakers of an 86-channel spherical loudspeaker array in an anechoic chamber, onto which virtual reverberation sources were mapped using vector base amplitude panning. It was tested whether listeners can distinguish lower spatial resolutions of reproduction of late reverberation from the highest achievable spatial resolution in different simulated rooms. The rendering of early reflections remained unchanged. The coherence of the sound field across a pair of microphones at ear and behind-the-ear hearing device distance was assessed to separate the effects of number of virtual sources and loudspeaker array geometry. Results show that between 12 and 24 reverberation sources are required for the rendering of late reverberation in virtual acoustic environments.

Perception of Surrounding Sound Source Trajectories in the Horizontal Plane: A Comparison of VBAP and Basic-Decoded HOA

Despite the fundamental role played by sound in multiple virtual reality contexts, few studies have explored the perception of virtual sound source motion in the acoustic space. The goal of this study was to compare the localization of virtual moving sound sources rendered with two different spatialization techniques: Vector BaseAmplitude Panning (VBAP) and fifth-order Ambisonics (HOA), both implemented in a soundproofed room and in their most basic form (basic decoding of HOA, VBAP without spread parameter). The perception of virtual sound trajectories surrounding untrained subjects (n=23) was evaluated using a new method based on a drawing-augmented multiple-choice questionnaire. In the spherical loudspeaker array used in this study, VBAP proved to be a robust spatialization technique for sound trajectory rendering in terms of trajectory recognition and height perception. In basic-decoded HOA, subjects exhibited far more disparate trajectory recognition and height perception performances but performed better in perceiving sound source movement homogeneity.

Elicitation of Expert Knowledge to Inform Object-Based Audio Rendering to Different Systems

Object-based audio presents the opportunity to optimise audio reproduction for different listening scenarios. Vector base amplitude panning (VBAP) is typically used to render object-based scenes. Optimizing this process based on knowledge of the perception and practices of experts could result in significant improvements to the end user's listening experience. An experiment was conducted to investigate how content creators perceive changes in the perceptual attributes of the same content rendered to systems with different numbers of channels, and to determine what they would do differently to standard VBAP and matrix based downmixes to minimize these changes. Text mining and clustering of the content creators' responses revealed 6 general mix processes: the spatial spread of individual objects, EQ and processing, reverberation, position, bass, and level. Logistic regression models show the relationships between the mix processes, perceived changes in perceptual attributes, and the rendering method/speaker layout. The relative frequency of use for the different mix processes was found to differ between categories of audio object suggesting that any downmix rules should be object category specific. These results give insight into how object-based audio can be used to improve listener experience and provide the first template for doing this across different reproduction systems.

A Low-Frequency Panning Method With Compensation for Head Rotation

Amplitude panning produces interaural time difference (ITD) cues that help localize images in directions between loudspeakers. However, if the panning gains are static, then the ITD cues produced in this way vary inconsistently as the listener's head rotates, compared with a real source, and so the dynamic ITD cues are inaccurate. This effect destabilizes the perception of the image and overall scene, and is worse for loudspeakers that are more widely spaced relative to the listener. Based on a simple head model that is accurate in the low-frequency ITD regime, the ITD is calculated for a general field, including those produced by panning. A simple formula is derived relating head orientation, image direction, and a field description vector. Panning functions are then found that compensate for head orientation and are valid for any image direction. For the special case when the listener is facing the image, the functions are equivalent to vector base amplitude panning. The performance is first assessed objectively using measured binaural responses, rather than the simple head model. Subjective comparison is then made with pre-existing listening tests and new listening tests in which the listener's head is tracked to control the panning gains in real-time. These show that images can be stabilized as predicted, and, furthermore, that with the same panning functions, images can be produced in all directions using two loudspeakers placed in front.

Sparse $\ell _{1}$-Optimal Multiloudspeaker Panning and Its Relation to Vector Base Amplitude Panning

Panning techniques, such as vector base amplitude panning (VBAP), are a widely used practical approach for spatial sound reproduction using multiple loudspeakers. Although limited to a relatively small listening area, they are very efficient and offer good localization accuracy, timbral quality, as well as a graceful degradation of quality outside the sweet spot. The aim of this paper is to investigate optimal sound reproduction techniques that adopt some of the advantageous properties of VBAP, such as the sparsity and the locality of the active loudspeakers for the reproduction of a single audio object. To this end, we state the task of multiloudspeaker panning as an ${\ell _{1}}$ optimization problem. We demonstrate and prove that the resulting solutions are exactly sparse. Moreover, we show the effect of adding a nonnegativity constraint on the loudspeaker gains in order to preserve the locality of the panning solution. Adding this constraint, ${\ell _{1}}$ -optimal panning can be formulated as a linear program. Using this representation, we prove that unique ${\ell _{1}}$ -optimal panning solutions incorporating a nonnegativity constraint are identical to VBAP using a Delaunay triangulation for the loudspeaker setup. Using results from linear programming and duality theory, we describe properties and special cases, such as solution ambiguity, of the VBAP solution.

Multi-channel loudspeaker reproduction and virtual acoustic environments in the context of hearing aid evaluation

Virtual acoustic environments reproduced via multiple loudspeakers are increasingly used for evaluating hearing aids in complex acoustic conditions. To further establish the feasibility of this approach, this study investigated the interaction between spatial resolution of different reproduction methods and technical and perceptual hearing aid performance measures using computer simulations. Three spatial audio reproduction methods—discrete speakers, vector base amplitude panning and higher order ambisonics—were compared in regular circular loudspeaker arrays with 4 to 72 channels. The influence of reproduction method and array size on performance measures of multi-microphone hearing aid algorithm classes with spatially distributed microphones and a representative single channel noise-reduction algorithm was analyzed. In addition to the analysis of reproduction methods, algorithm performance was tested in a number of different virtual acoustic environments in order to assess the underlying factors of decr...

Modeling Localization of Amplitude-Panned Virtual Sources in Sagittal Planes.

Vector-base amplitude panning (VBAP) aims at creating virtual sound sources at arbitrary directions within multichannel sound reproduction systems. However, VBAP does not consistently produce listener-specific monaural spectral cues that are essential for localization of sound sources in sagittal planes, including the front-back and up-down dimensions. In order to better understand the limitations of VBAP, a functional model approximating human processing of spectro-spatial information was applied to assess accuracy in sagittal-plane localization of virtual sources created by means of VBAP. First, we evaluated VBAP applied on two loudspeakers in the median plane, and then we investigated the directional dependence of the localization accuracy in several three-dimensional loudspeaker arrangements designed in layers of constant elevation. The model predicted a strong dependence on listeners' individual head-related transfer functions, on virtual source directions, and on loudspeaker arrangements. In general, the simulations showed a systematic degradation with increasing polar-angle span between neighboring loudspeakers. For the design of VBAP systems, predictions suggest that spans up to 40° polar angle yield a good trade-off between system complexity and localization accuracy. Special attention should be paid to the frontal region where listeners are most sensitive to deviating spectral cues.

Evaluation of Spatial Audio Reproduction Schemes for Application in Hearing Aid Research

Loudspeaker-based spatial audio reproduction schemes are increasingly used for evaluating hearing aids in complex acoustic conditions. To further establish the feasibility of this approach, this study investigated the interaction between spatial resolution of different reproduction methods and technical and perceptual hearing aid performance measures using computer simulations. Three spatial audio reproduction methods -- discrete speakers, vector base amplitude panning and higher order ambisonics -- were compared in regular circular loudspeaker arrays with 4 to 72 channels. The influence of reproduction method and array size on performance measures of representative multi-microphone hearing aid algorithm classes with spatially distributed microphones and a representative single channel noise-reduction algorithm was analyzed. Algorithm classes differed in their way of analyzing and exploiting spatial properties of the sound field, requiring different accuracy of sound field reproduction. Performance measures included beam pattern analysis, signal-to-noise ratio analysis, perceptual localization prediction, and quality modeling. The results show performance differences and interaction effects between reproduction method and algorithm class that may be used for guidance when selecting the appropriate method and number of speakers for specific tasks in hearing aid research.

Is Sensorimotor BCI Performance Influenced Differently by Mono, Stereo, or 3-D Auditory Feedback?

Imagination of movement can be used as a control method for a brain-computer interface (BCI) allowing communication for the physically impaired. Visual feedback within such a closed loop system excludes those with visual problems and hence there is a need for alternative sensory feedback pathways. In the context of substituting the visual channel for the auditory channel, this study aims to add to the limited evidence that it is possible to substitute visual feedback for its auditory equivalent and assess the impact this has on BCI performance. Secondly, the study aims to determine for the first time if the type of auditory feedback method influences motor imagery performance significantly. Auditory feedback is presented using a stepped approach of single (mono), double (stereo), and multiple (vector base amplitude panning as an audio game) loudspeaker arrangements. Visual feedback involves a ball-basket paradigm and a spaceship game. Each session consists of either auditory or visual feedback only with runs of each type of feedback presentation method applied in each session. Results from seven subjects across five sessions of each feedback type (visual, auditory) (10 sessions in total) show that auditory feedback is a suitable substitute for the visual equivalent and that there are no statistical differences in the type of auditory feedback presented across five sessions.

Spatial Audio System for Surround Video

In this paper we present the design processes of a spatial audio system for Surround Video. Surround Video is a method of reproducing two simultaneous video streams captured by two cameras onto a main television screen and onto the walls of a room via a projector. Through the use of distortion software to correctly map the surround image to the geometry of the viewing room, the user experiences 180 degrees of video reproduction, immersing them in the content. The design of a spatial audio system was necessary to give 360 degree coverage of audio so that, like for the video, the viewer is immersed into the programme world. We discuss the design process and decisions made that concluded in using a mixed reproduction system of Vector Base Amplitude Panning with Ambisonics to match the audio localisation precision with the video precision; high localisation around the main monitor image whilst the surrounding audio is immersive, but with less localisation. Attributes associated with objects in the real world are discussed and methods for recreating the effect of distance, in-head panning, sound scene rotations, reverberation and movement that alter the reverberation placement are presented. The end result is an immersive video and audio system that can be used by the BBC Research & Development department to demonstrate the potential of such technologies where the audio system uses 14 loudspeakers, a subwoofer signal and a discrete ‘4D’ type effects channel.

Providing Surround Sound with Loudspeakers: A Synopsis of Current Methods

Available methods for room-related sound presentation are introduced and evaluated. A focus is put on the synthesis side rather than on complete transmission systems. Different methods are compared using common, though quite general criteria. The methods selected for comparison are: INTENSITY STEREOPHONY after Blumlein, vector-base amplitude panning (VBAP), 5.1-SURROUND and its discrete-channel derivatives, synthesis with spherical harmonics (AMBISONICS, HOA), synthesis based on the boundary method, namely, wave-field synthesis (WFS), and binaural-cue selection methods (e.g., DIRAC). While VBAP, 5.1-SURROUND and other discrete-channel-based methods show a number of practical advantages, they do, in the end, not aim at authentic sound-field reproduction. The so-called holophonic methods that do so, particularly, HOA and WFS, have specific advantages and disadvantages which will be discussed. Yet, both methods are under continuous development, and a decision in favor of one of them should be taken from a strictly application-oriented point of view by considering relevant application-specific advantages and disadvantages in detail.

Motion simulation in the environment for auditory research

Virtual sound source motion has been implemented in the Army Research Laboratory's Environment for Auditory Research, which contains a 57-channel spherical loudspeaker array located in an anechoic chamber. Using the Psychophysics Toolbox Version 3 low-latency PortAudio API, 57 channels of streaming audio are dynamically updated in real-time using MATLAB for signal processing. Both distance-based amplitude panning (DBAP) and vector base amplitude panning (VBAP) have been implemented in MATLAB for controlling source motion. Sources are defined on a given path, such as a circle, ellipse, or the “dog bonex”; flight pattern often used in aviation. While DBAP works convincingly for virtual sources located on the sphere defined by the loudspeaker array, VBAP is needed to position sources outside the array. Source motion paths are defined parametrically with respect to time, and playback buffers update the panned position every 11.6 ms. Based on the source's instantaneous distance, diffuse-field or free-field amplitude attenuation is added in MATLAB as well air absorption filtering. This system will be used for a variety of audio simulations and auditory experiments.

실내 환경에서 쾌적성 향상을 위한 Vector Base Amplitude Panning 기반의 소음제어

A variety of noise control methods have been developed as an interest on noise issues increases. Among them, noise control methods using masking effect, a phenomenon to reduce the ability to notice the unwanted sound by proper sound, to implement a pleasant sound environment have been studied under the name of soundscape. We proposed a novel vector base amplitude panning(VBAP) based noise control method to apply to the building environment. The proposed method could improve the amenity inside the building to reproduce the sounds with excellent masking effect on the incoming path of noise using the control speakers, considering the direction of noise source. The directional masking sounds can be generated by using VBPA technique. To verify the performance of the proposed method, we carried out the subjective test for the degree of amenity according to direction of the masking sound. Subjective test results showed that it is possible to improve the amenity inside the building by controlling the direction of masking sound considering the human`s auditory characteristic.

Acoustic performance of an installed real‐time three‐dimensional audio system—Part II.

The exterior effects room (EER), located at the NASA Langley Research Center, was recently upgraded to allow for simulation of aircraft flyovers in a three‐dimensional (3‐D) audio and visual environment. The 3‐D audio server employs an implementation of the vector base amplitude panning (VBAP) method to position virtual sources at arbitrary azimuth and elevation angles in the EER. Recent work focused on the development of loudspeaker equalization first using high order FIR filters [POMA 9 015004 (2010)], and later using low order IIR filters [J. Acoust. Soc. Am. 128 2482 (2010)]. The latter, in conjunction with full‐path time delay compensation and relative gain compensation, were implemented in real‐time and shown to reproduce the desired sound field to within about ±5 dB over an extended frequency range for stationary and moving sources. In the present work, the performance is further characterized both objectively and subjectively. Addressed are calibration of the system for absolute sound pressure level reproduction and measurement of the spatial uniformity of the generated sound field. Further, localization of sound sources will be subjectively measured to assess the efficacy of the VBAP implementation in the EER.

Acoustic performance of an installed real‐time three‐dimensional audio system.

The Exterior Effects Room (EER), located at the NASA Langley Research Center, is a facility built for psychoacoustic studies of aircraft community noise. Recently, the EER was significantly upgraded to allow for simulation of aircraft flyovers in a three-dimensional audio and visual environment. The upgrade included installation of 27 satellite and 4 subwoofer loudspeakers that are driven by a real-time audio server. The audio server employs an implementation of the Vector Base Amplitude Panning (VBAP) method to position virtual sources at arbitrary azimuth and elevation angles in the EER. Real-time application of filters, time delays, and gains are required to compensate for installation effects, including those associated with the irregular room geometry, colorization due to varying loudspeaker installations, and crossover filtering. The authors previously showed [J. Acoust. Soc. Am., 127, 1969 (2010)] that color compensation and crossover filtering could be achieved for satellite and subwoofer loudspeakers. However, the resulting FIR filters were too long (32,768 taps) to implement in real-time. The focus of this work is on development of reduced-length surrogate IIR filters and on measurement of the acoustic performance of the installed real-time system.