Multichannel Sound Reproduction Research Articles

Direct acoustic velocity vector measurements for evaluation of multichannel sound reproduction systems with signals of varied partial coherence

In multichannel sound reproduction systems, the perceived virtual auditory scene is strongly influenced by inter-channel phase-shifts and the degree of mutual coherence among channel signals. Such degrees of freedom may be employed to effect an expanded virtual sound stage or a sense of spaciousness, but they also may lead to unwanted spectral coloration, diffuse or ambiguous virtual source locations, or startling and disorienting spatial image perceptions often described as “phaseyness.” Such effects may be described and understood in terms of the acoustic velocity in the vicinity of the listener. In this work we present theoretical predictions of the acoustic velocity vector for a stereo reproduction system with channel signals of varying phase and levels of mutual coherence, and we report direct measurements of the acoustic velocity vector employing a 3D sound intensity probe for several specific cases. Acoustic velocity vector predictions and measurements also are correlated with listener perceptions. The presented measurements are also compared to subjective localization of sound sources. The direct measurement of the acoustic velocity vector in spatial sound reproduction systems is a useful tool to quantitatively evaluate the performance of multi-channel spatial audio reproduction systems, to predict listener perceptions of the acoustic field reproduced by such systems, and to investigate the impact of early reflections in a room on localization.

Estimation of insertion loss for noise barrier with multichannel sound reproduction technology

A method based on the wave field synthesis is proposed to estimate the insertion loss of a noise barrier under the complex diffracted sound field due to the characteristics of the noise source and the transmitted sound through the barrier. This method is equivalent to evaluating the acoustical performance of the noise barrier in a reproduced sound field. There are two advantages of the proposed method. First, by storing the radiated sound of various noise sources as a database in advance, the insertion loss for them can be obtained. Second, the impulse responses from multipoint can be measured by changing one loudspeaker position sequentially, so it does not necessarily require many loudspeakers. In order to validate this method, numerical simulation was performed for a diffracted sound field consisting of a point source and a rigid barrier. Moreover, the insertion loss of simple noise barriers for one loudspeaker was estimated under the primary and synthesized sound field conditions experimentally. As a practical example, the insertion loss of the same noise barriers for a moving automobile was also estimated. The results show that the estimation error is within a few decibels in the frequency band where spatial aliasing does not occur.

Surrounding line sources optimally reproduce diffuse envelopment at off-center listening positions.

Listener envelopment has previously been studied in the fields of room acoustics and multichannel sound reproduction. However, the potentially detrimental effect of a directional imbalance remains uninvestigated. This paper presents a listening experiment under anechoic conditions using a ring of 24 loudspeakers. Participants rated perceived envelopment for various loudspeaker subsets fed by incoherent noise signals. Off-center listening positions were simulated for different acoustic source models: -6 dB (point source), -3 dB (line source), or 0 dB attenuation for every doubling of distance. Only the line-source model preserved envelopment off-center, providing a low interaural level difference and a low interaural coherence as perceptual cues.

Perceptual validation of sound environment reproduction inside an aircraft mock-up

Auditory comfort evaluations are garnering increased attention in engineering and particularly in the context of air transportation. Being able to produce sound environments corresponding to various flight conditions in aircraft mock-ups would be a valuable tool to investigate acoustic comfort inside aircrafts in controlled environments. Before using such mock-ups, they must be developed and validated in physical and perceptual terms. This paper provides a perceptual validation of sound environment reproduction inside aircraft mock-up. To provide a faithfully reproduced sound environment, time, frequency and spatial characteristics should be preserved. Physical sound field reproduction approaches for spatial sound reproduction are required while properly preserving localization cues at the listener's ears to recreate a realistic and immersing sound environment. We report a perceptual validation of a sound field reproduction system developed in an aircraft mock-up based on multichannel least-square methods and equalization. Twenty participants evaluated reproduced sound environments relative to a reference sound environment in an aircraft cabin mock-up equipped with a 41-actuator multichannel sound reproduction system. Results indicate that the preferred reproduction corresponds to the best physical reconstruction of the sound environment.

Analysis of partially coherent acoustic wavefields from multichannel sound reproduction systems

This work analyzes the performance of multichannel sound reproduction systems using the theory of partially coherent wavefields to model the acoustic velocity vector at the listener’s location. In this framework, the original signal is modelled as a narrowband, locally stationary random process, defined by a coherence time. The system model incorporates attenuation and delays from both positioning of the listener relative to the loudspeakers and any processing used in the reproduction system (e.g., panning). Given the finite coherence time of the signal, the magnitude and direction of the resultant velocity vector fluctuates in time. The location and spread of the virtual source that a human listener infers is determined by the distribution of velocity vector directions and a psychoacoustic averaging time associated with the precedence effect. Using this framework, we demonstrate the relative importance of three time constants in forming a stable image of the source location: the signal coherence time, the acoustic decay time, and the perceptual averaging time. This framework can be extended to incorporate early reflections in the listening environment and generalized to encompass natural sounds, such as speech or music, which can be modelled as a sum of narrowband components.

Analysis of and Experiments on Vertical Summing Localization of Multichannel Sound Reproduction with Amplitude Panning

Analysis of and Experiments on Vertical Summing Localization of Multichannel Sound Reproduction with Amplitude Panning

Using mobile sound to explore spatial relationships between dance and music performance

ABSTRACTThe availability of robust and cheaper hardware tools in recent years has allowed the possibility of effectively integrating spatial sound as an organic component of dance and music performance projects. Inspired by these recent developments, an original body-worn sound system was designed, implemented and acoustically optimized aiming to effectively integrate performers’ movements and amplified sounds on stage. An innovative acoustic measurement method was used in connection with tests and interviews with practitioners to assess various sonic and artistic features of the implemented sound vest prototype. Audience questionnaires were employed to assess the perceived acoustic performance of the system in a medium size dance studio. Survey results showed that the perceived acoustic performance of the sound vest is highly dependent on the types of sound materials radiated by the system, as well as on the position of the performer in a room. Future work will consider the implementation and assessment of an extended hybrid spatial system consisting of several mobile sound sources synchronized with a fixed multi-channel sound reproduction system.

Sound-field measurement with moving microphones.

Closed-room scenarios are characterized by reverberation, which decreases the performance of applications such as hands-free teleconferencing and multichannel sound reproduction. However, exact knowledge of the sound field inside a volume of interest enables the compensation of room effects and allows for a performance improvement within a wide range of applications. The sampling of sound fields involves the measurement of spatially dependent room impulse responses, where the Nyquist-Shannon sampling theorem applies in the temporal and spatial domains. The spatial measurement often requires a huge number of sampling points and entails other difficulties, such as the need for exact calibration of a large number of microphones. In this paper, a method for measuring sound fields using moving microphones is presented. The number of microphones is customizable, allowing for a tradeoff between hardware effort and measurement time. The goal is to reconstruct room impulse responses on a regular grid from data acquired with microphones between grid positions, in general. For this, the sound field at equidistant positions is related to the measurements taken along the microphone trajectories via spatial interpolation. The benefits of using perfect sequences for excitation, a multigrid recovery, and the prospects for reconstruction by compressed sensing are presented.

Attempt to evaluate sound absorption characteristics of material with multichannel sound field reproduction system

Attempt to evaluate sound absorption characteristics of material with multichannel sound field reproduction system

Living Stereo: Histories and Cultures of Multichannel Sound eds. by Paul Théberge, Kyle Devine, and Tom Everrett

Stereo: Histories and Cultures of Multichannel Sound. Edited by Paul Theberge, Kyle Devine, and Tom Everrett. New York: Bloomsbury Academic, 2015. [viii, 289 p. ISBN 9781623565169 (hardcover), $120; ISBN 9781623566654 (paperback), $29.95; ISBN 9781623566876 (PDF ebook), $25.99; ISBN 9781623565510 (EPUB e-book), $25.99.] Figures, timeline, bibliographic references, index. At a casual glance a reader might be tempted to ask, there really a need for an entire book on stereo? Stereo and multichannel sound is so pervasive in our lives today, and technology is so easily available, one might feel comfortable taking it for granted. But what does one really know about how, when, and why stereo was developed? How did it become norm for average listener? In my work with stage production and media room designers, I found that even professionals configure stereo setups as two speakers placed on left and right of a projection screen fed from a single mono sound source, unaware that stereo actually requires two discrete audio channel outputs. Such situations demonstrate that there is an ongoing need for both a surface and deeper understanding of stereo. A book addressing this issue is well timed, as generation of people involved in evolution of stereo is aging and many students and young professionals did not grow up during an era when stereo was rare and not an expectation (whether it be mono LPs in early 1960s or even mono TVs that were standard well into 1980s). In spring 2012, Sound Studies Group at Institute for Comparative Studies in Literature, Art & Culture organized a conference, Living Stereo: History, Culture, Multichannel that challenged presenters to reflect on the history and significance of stereo sound reproduction in aural culture. The call for conference presentations noted that although the whole culture and industry of music and sound became organized around principle of stereo during mid twentieth century ... nothing about this--not invention or acceptance or ubiquity of stereo--was inevitable. Nor did aesthetic conventions, technological objects, and listening practices required to make sense of stereo emerge fully formed, out of blue (from http://www.iaspm.net /living-stereo-history-culture-multichannelsound/ [accessed February 20, 2017]. The original link to conference call at http://carleton.ca/icslac/livingstereo is no longer active). Casting a wide net, organizers solicited contributions from researchers in disciplines ranging from popular music, musicology, ethnomusicology, sound and media studies, sociology, gender studies, film theory, to science and technology studies. A key result of this symposium was publication of Stereo: Histories and Cultures of Multichannel Sound, which consists of a substantial introductory chapter and eleven essays written by fifteen authors with expertise in a variety of disciplines. Starting from common but broad theme of history and significance of multichannel sound reproduction, individual essays cover a range of topics and address aspects of research, technical development, history, and culture of multichannel sound playback. In Introduction: Stereo, editors note that given significance and even, perhaps, centrality of stereophony in contemporary musical and acoustic culture, it is surprising that stereo's widespread aesthetic, social and economic implications have been largely ignored in music, sound, and media studies (p. 1). After reading through book and its extensive reference list as well as searching other web, WorldCat, and journal resources, it is clear to me this is first book to pull together a significant collection of historical, cultural, and musical research on this topic. While each chapter overlaps with a variety of fields of study, what is common to all of chapters is that they intersect, in one way or another, with interdisciplinary field of sound studies. …

Investigation of auditory distance perception and preferences in concert halls by using virtual acoustics.

Virtual acoustics with multichannel sound reproduction was used to study auditory distance perception in four concert halls with multiple sound sources on stage. Eight subjects reported apparent auditory distances in five seating positions from 10 to 26 m to the middle of the sources on stage. The distance estimates were collected by absolute distance estimation procedure as well as a free modulus estimation procedure including both within and between halls evaluations. In addition, pairwise preferences were collected for two positions within each hall and for one position between halls. Results reveal that the perception of distance is dependent on the hall acoustics and show how the strength factor G and direct-to-reverberant energy ratio covary in relation to perceptual distances in these halls. The results also indicate that in such large spaces the overestimation of short distances may continue up to and further than 10 m from the sound sources. Preference results show that closer seats were liked more than further ones and that the strength of this preference is associated with the difference in perceptual distances.

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.

Multichannel Sound Reproduction Quality Improves with Angular Separation of Direct and Reflected Sounds

Multichannel Sound Reproduction Quality Improves with Angular Separation of Direct and Reflected Sounds

Optimizing the Similarity of Loudspeaker–Room Responses in Multiple Listening Positions

A shortcoming of multichannel sound reproduction standards, such as stereo or 5.1 surround, is their incompatibility with multiple off-axis listening positions. Accurate reproduction of virtual sound sources can only be experienced in the sweet spot, which is located equidistant to the loudspeakers. We here present a novel methodology to compensate audio systems such that the channel similarity is optimized in several listening positions simultaneously. To that end we propose a novel MIMO personal audio filter design framework based on feed-forward control. By proper design choices, filters that successfully compensate for multiple off-axis positions and irregularities in the frequency sum responses are obtained. The design choices include allpass filters with appropriate phase shifts as target for each listening position in addition to a weighted similarity requirement. Evaluations based on measurements of two four-channel car audio systems show that the proposed method significantly improves timbral sound reproduction and phantom center reproduction in several listening positions simultaneously.

Sound Reproduction Loudspeakers and Rooms

Floyd Toole, seorang ahli terkemuka di bidang reproduksi suara, dalam bukunya ia menjelaskan bagaimana merancang desain audio agar dapat terdengar sebaik mungkin terutama untuk ruang kontrol rekaman dan sistem hiburan di rumah. Kerja yang komprehensif ini mencakup seluruh rangkaian reproduksi suara dari multi-channel konfigurasi audio dan sistem loudspeaker / ruang untuk akustik dan psychoacoustics dan proses mengevaluasinya. Bagian 1 menunjukkan kepada pembaca bagaimana untuk menciptakan pengalaman mendengarkan suara yang terbaik, menawarkan pendekatan praktis untuk rangkaian reproduksi suara. Bagian 2 dan 3 merupakan pertimbangan mendalam tentang akustik dan psychoacoustics.

Sound Reproduction System Robust against Environmental Variation by Switching Control Band Range

A robust multichannel sound reproduction system that utilizes the relationship between the width of the actual control area and the control frequency of the control points is proposed. The reproduction accuracy of a conventional sound reproduction system is reduced by room environment variations when fixed inverse filter coefficients are used. This tendency becomes more significant when control points are arranged more closely. To resolve this problem, the frequency control band at every control point is switched to avoid degrading the reproduced sound in low frequencies, so the pass band range of the control points at both ears is only high-range. That of the other control points is the entire control range. Numerical simulation with real environmental data showed that improvement of the reproduction accuracy is about 6.1 dB on average, even with a temperature fluctuation of 5°C as an environmental variation in the listening room.

Active listening room compensation for massive multichannel sound reproduction systems using wave-domain adaptive filtering

The acoustic theory for multichannel sound reproduction systems usually assumes free-field conditions for the listening environment. However, their performance in real-world listening environments may be impaired by reflections at the walls. This impairment can be reduced by suitable compensation measures. For systems with many channels, active compensation is an option, since the compensating waves can be created by the reproduction loudspeakers. Due to the time-varying nature of room acoustics, the compensation signals have to be determined by an adaptive system. The problems associated with the successful operation of multichannel adaptive systems are addressed in this contribution. First, a method for decoupling the adaptation problem is introduced. It is based on a generalized singular value decomposition and is called eigenspace adaptive filtering. Unfortunately, it cannot be implemented in its pure form, since the continuous adaptation of the generalized singular value decomposition matrices to the variable room acoustics is numerically very demanding. However, a combination of this mathematical technique with the physical description of wave propagation yields a realizable multichannel adaptation method with good decoupling properties. It is called wave domain adaptive filtering and is discussed here in the context of wave field synthesis.

Sound reproduction system with switching control band range on every listening point

We propose a robust multichannel sound reproduction system that utilizes the relationship between the width of the actual listening area and the control frequency of the listening points. The conventional multichannel sound reproduction system uses inverse filters that are designed based on room transfer functions (RTFs) from loudspeakers to listening points in the listening room. However, the sound reproduction accuracy is deteriorated by room environment variations when fixed inverse filter coefficients are used because the condition number relevant to the instability of the matrix composed of the RTFs is large, especially at low frequencies; the inverse filters are unstable at those frequencies. This tendency is more remarkable when listening points are arranged more closely. To resolve the problem, we switch the control band at every listening point to avoid degrading the reproduced sound in low‐band frequencies. The control band range of the listening points at both ears is only high band. That of th...

The influence of changes in diffusive acoustical treatment on spatial imagery associated with multichannel sound reproduction

Listening experience in the newly constructed, largely diffuse small room at Blackbird Studios has led to the design of a new research space for the Sound Recording program in McGill University’s Schulich School of Music. The space was created to allow for experimental investigation of the influence of changes in diffusive acoustical treatment on variation in auditory imagery associated with multichannel sound selections while holding listener location and orientation constant relative to a fixed five-channel loudspeaker array. Preliminary tests suggest that a number of benefits result when low-amplitude indirect sound is provided by diffusive room acoustic treatment within the first 30 ms of the arrival of the loudspeaker signals. Both for conventional multitrack mixes, and for recordings made using multichannel microphone arrays, these benefits include greater Listener EnVelopment (LEV), improved segregation of simultaneously sounding musical sources, and more solid phantom images of virtual sources, especially those located to the listener’s extreme sides between front and rear loudspeakers (between 30 and 110 deg of azimuth to the left and right). This paper will summarize those results, and describe the specially designed system of variable acoustic treatment that enables such direct experimental investigation. [Work supported by Canada Foundation for Innovation.]

Loudspeakers and listening rooms, Part II: The perception of reflections

A review of the effects of reflections on perceptions of sound quality, direction, image size, spaciousness, speech intelligibility, etc., lending perspective to the matter of which elements might be perceptually important in multichannel sound reproduction systems. In general they appear to be less problematic than is commonly believed. This, combined with the considerable ability of listeners to adapt to certain auditory influences of small rooms, brings into question several popular practices in the design of loudspeakers and listening rooms. Anechoic measurements on loudspeakers that have been done in a manner that anticipates sound reproduction in rooms can be used to calculate a figure of merit. The correlation between the calculated ratings, and those resulting from double-blind listening tests, is high: 0.86. This has implications for the acoustical treatment of rooms, and to the necessity for controlling the sound field at low frequencies. Only then can there be any assurance that the art in recordings will be heard by consumers as it was created in control rooms.