Virtual Microphone Control Research Articles

Using binaural and spherical microphone arrays to assess the quality of synthetic spatial sound fields

Recently, we completed the Collaborative-Research Augmented Immersive Virtual Environment Laboratory (CRAIVE-Lab) with a usable floor area of 12 × 10 m2 at Rensselaer. The CRAIVE-Lab project addresses the need for a specialized virtual-reality (VR) system for the study and enabling of communication-driven tasks with groups of users immersed in a high-fidelity multi-modal environment located in the same physical space. For the acoustic domain, a 134-loudspeaker-channel system has been installed for Wave Field Synthesis (WFS) with the support of Higher-Order-Ambisonic (HoA) sound projection to render inhomogeneous acoustic fields. An integrated 16-channel spherical microphone array makes the CRAIVE-Lab an ideal test bed to study different spatial rendering techniques such as Wave-Field Synthesis, Higher-Order Ambisonics and Virtual Microphone Control (ViMiC). In this talk, sound-field measurements taken with a traditional binaural manikin will be compared to spherical microphone recordings to assess the quality of the different rendering techniques for large-scale labs. A focus will hereby be set on assessing the sweet spot area for different rendering techniques. [Work supported by NSF 1229391, NSF 1631674, and the Cognitive and Immersive Systems Laboratory (CISL).]

Spatialized sound reproduction for telematic music performances in an immersive virtual environment

Telematic performances connect musicians and artists at remote locations to form a single cohesive piece. As these performances become more ubiquitous as more people have access to very high-speed Internet connections, a variety of new technologies will enable the artists and musicians to create brand new styles of works. The development of the immersive virtual environment, including Rensselaer Polytechnic Institute's own Collaborative-Research Augmented Immersive Virtual Environment Laboratory, sets the stage for these original pieces. The ability to properly spatialize sound within these environments is important for having a complete set of tools. This project uses a local installation to exemplify the techniques and protocols that make this possible. Using the visual coding environment MaxMSP as a receiving client, patches are created to parse incoming commands and coordinate information for engaging sound sources. Their spatialization is done in conjunction with the Virtual Microphone Control system, which is then mapped to loudspeakers through a patch portable to various immersive environment setups.

좌석의 정음공간 형성을 위한 가상마이크로폰 기반 능동음향제어 기법 연구

ABSTRACT In this study, theoretical and experimental analyses were performed for creating and moving the zone of quiet(ZoQ) to the ear location of a sitter by using active sound control technique. As the ZoQ is actively created at the location of the error microphone basically with an active sound con-trol system using an algorithm such as the filtered-x least mean square(FxLMS), the virtual micro-phone control(VMC) method was considered to move the location of the ZoQ to around the sitter`s ear. A chair system with microphones and loudspeakers on both sides was manufactured for the ex-periment and thus an active headrest against the swept narrowband noise as the primary noise was implemented with a real-time controller in which the VMC algorithm was embedded. After the con-trol experiment with and without the VMC method, the location variation of the ZoQ by analyzing the error signals measured by the error and the virtual microphones. Therefore, it is observed that the FxLMS with the VMC technique can provide the re-location of the ZoQ from the error micro-phone location to the virtual microphone location. Also it is found that the amount of the attenu-ation difference between the two locations was small.

Nonlinear active noise control for headrest using virtual microphone control

In this paper, a feed-forward nonlinear active noise control algorithm is developed using the Filtered-S LMS (FSLMS) algorithm and virtual microphone control for an active headrest application. Virtual microphone control is implemented to attenuate noise at the ears of the headrest occupant using the physical microphones placed at remote locations. The proposed nonlinear virtual microphone control algorithm is verified in real-time in a headrest. Different nonlinear noise processes are studied and it is shown that in all cases, the FSLMS algorithm outperforms the FXLMS algorithm in controlling nonlinear primary noise at a virtual location.

The effect of listener head movement on perceived envelopment and apparent source width

Current research examining listeners' perceived spatial impression of a concert hall relies on a fixed-head worldview, since the overwhelming majority of listening tests conducted to determine subjective spaciousness [listener envelopment (LEV) and apparent source width (ASW)] has required listeners to keep their heads fixed. Such a worldview is an incomplete one, because listeners make noticeable exploratory head movements while evaluating sonic environments, including the more common task of source localization as well as the more involved task of evaluating the spaciousness of a concert hall. This study investigates the role of listener head movement in the evaluation of perceived LEV and ASW under 15 different concert hall conditions simulated over eight loudspeakers using Virtual Microphone Control. The conditions consist of both varying ratios of front-to-back energy and varying levels of cross-correlated reverberant energy. Head movements are monitored in terms of angular rotation (azimuth, elevation, and roll) using a head tracker while listeners are prompted to give subjective ratings of LEV and ASW ranging from 1 (least) to 7 (most). The listening tests are then repeated while subjects are asked to keep their heads fixed. The head movements are analyzed and results of the tests are compared.

A Cinematic Spatial Sound Display for Panorama Video Applications

This paper describes a new sound spatialisation system which is an integral part of Rensselaer Polytechnic Institute’s new Experimental Media and Performing Arts Center (EMPAC). The Cinematic Spatial Sound Display (CSSD) was originally conceived for interactive panorama video installations, but the architecture goes beyond this particular application. The CSSD is characterised by its scalability to various loudspeaker configurations. It spatialises sound from dry sound files or live sources using control data that describe the spatial scenes. The time lines for source positions and other experimental parameters can be stored and edited in the CSSD, and the system can also process live user input to control selected parameters. The CSSD is more than just a sound positioning tool, and the underlying Virtual Microphone Control (ViMiC) technology was developed to support artists in designing new forms of spatial imagery. The software enables the user to create computer-generated rooms with virtual microphones and sound sources. The algorithm uses physical laws to auralise acoustic scenes – allowing realistic effects such as the Doppler shift and the simulation of various classical microphone techniques. Various parameters of ViMiC can be adjusted in real time, including the directivity patterns and orientations of both the microphones and sound sources as well as their precise locations. Surreal scenes can be created by assigning artificial directivity patterns to microphones or changing the laws of physics in the model. An algorithm to extract the sound-source positions in recordings using a microphone array is also part of the CSSD. The algorithm was specifically designed to operate in multiple sound-source scenarios and can also be used for telematic music applications.

Analog Active Control of Acoustic Noise at a Virtual Location

In this brief, an analog virtual microphone control system in application to noise reduction for a phone is designed. It aims at generating a zone of quiet at a virtual microphone location corresponding to the eardrum. Such location is different than the real microphone location. The idea of the control system is based on the assumption that the primary acoustic noise is the same at these two locations. The first constraint is formulated to guarantee a sufficient stability margin. Another constraint protects against excessive noise reinforcement for any frequency. Controller parameters are found by solving the optimization problem. Due to its high nonlinearity the exhaustive search method is used. It follows a preliminary analysis of the solution space. Additionally, a feedforward filter compensating for influence of the control system on the transmitted speech is designed. The overall control system is implemented using chips with switched capacitors, what makes the tuning and maintenance easy. The system is verified by means of simulations and real-world experiments. It is shown that road noise is satisfactorily reduced. Both measurement results and subjective impressions confirm that the system meets the requirements.

A Loudspeaker-Based Projection Technique for Spatial Music Applications Using Virtual Microphone Control

This article describes a new sound-projection sys- tem for multichannel loudspeaker setups that has been developed by the authors. The system, called Virtual Microphone Control (ViMiC), is based on the simulation of microphone techniques and acoustic enclosures. In auditory virtual environments (AVEs), it is often required to position an anechoic point source in three-dimensional space. When sources in such applications are to be displayed using mul- tichannel loudspeaker reproduction systems, the processing is typically based upon simple amplitude- panning laws. With an adequate loudspeaker setup, this approach allows relatively accurate positioning of spatial images in the horizontal plane, but it lacks the flexibility many composers of computer music would like to have. This article describes an alternative approach based on an array of virtual mi- crophones. In the newly designed environment, the microphones, with adjustable directivity patterns and axis orientations, can be spatially placed as de- sired. Each virtual microphone signal is then fed to a separate (real) loudspeaker for sound projection. The system architecture was designed for a maximum flexibility in the creation of spatial imagery. Despite its flexibility, the system is intuitive to use because it is based on the geometrical and physical principles of microphone techniques. It is also consistent with the expectations of audio engineers to create sound imagery similar to that associated with standard sound-recording practice, but it goes beyond the original concept by allowing strategic violations of physically possible parameters; namely, new supernatural microphone directivity patterns can be implemented into the ViMiC system. This article begins with a review of various microphone techniques on which the ViMiC system Computer Music Journal, 32:3, pp. 55-71, Fall 2008 c � 2008 Massachusetts Institute of Technology. relies and alternative sound-projection techniques. Next, the fundamental physical concepts on which the ViMiC system is based are described. In the following section, software implementation of the system is outlined with a focus on strategies to keep processor load and system latency low. The article concludes with a description of several projects that involved the ViMiC system.

Virtual microphone control: A comparison of measured to created impulse responses of various microphone techniques

A method of rendering sound sources in 3-D space has been developed using virtual microphone control (ViMiC) [J. Acoust. Soc. Am. 117, 2391]. This method has been used to create a flexible architecture for the creation and rendering of a virtual auditory environment based on microphone techniques. One of the advantages of ViMiC is the ability to simulate coincident, near-coincident, and spaced microphone recording techniques. This allows the user active spatial control over the recorded environment and the ability to shape the final rendering based on his or her specific auditory needs. In order to determine the accuracy of simulating the virtual microphone techniques, measurements of several acoustic spaces in Troy, NY will be compared to the measurements of generated impulse responses of the same modeled spaces within the ViMiC environment. The data from the measured impulse responses will be used to adapt the ViMiC system in order to create a more realistic auditory rendering. Moreover, the ViMiC system can be improved for use as an educational tool for teaching recording engineers to hear the subtle differences between various microphone techniques.

Acoustic rendering of a virtual environment based on virtual microphone control and binaural room scanning

Binaural room scanning (BRS) is a convolution technique that utilizes a set of spatially indexed impulse responses that are selected in response to listener head movements during virtual acoustic rendering, such that the direction of sonic elements is automatically updated according to the angle determined by a head tracker. Since the room impulse responses have to be measured for only a few loudspeaker positions, a very successful application of BRS is the simulation of a control room. In order to create a flexible headphone‐based virtual environment, it is proposed to simulate the input signals for the BRS system using virtual microphone control (ViMiC). ViMiC renders a virtual environment by simulating the output signals of virtual microphones that can be used to address a surround loudspeaker system. The advantages of this approach are twofold. First, the measured impulse responses of the BRS system ensure high spatial density in overall reflection patterns, avoiding the typical gaps in between the early reflections that occur when using solely mirror images or ray tracing. Second, the resulting imaging is closer to common audio engineering practice, where a pleasant but plausible environment is favored over a more purely realistic rendering.

A hybrid approach to rendering multichannel audio, using wave-field synthesis and stereophonic techniques, with virtual microphone control

In the evolution of multichannel audio presentation, a number of formats have emerged including 5.1 surround and wave-field synthesis (WFS). Due to the complexity and number of components required to realize an immersive WFS system, the use in a home theater environment is currently impractical. This study aims to investigate the perceptual advantages of integrating both systems into a hybrid array capable of providing immersive sound for a number of listeners, at a scale that is attainable for the consumer in terms of budget and complexity. In this approach the three front speakers (left, center, and right) are replaced with a linear line array allowing for a better lateral and depth imaging, while increasing the sweet spot. The rendering will be created using Virtual Microphone Control (ViMiC) for both WFS, simulating a line of omnidirectional microphones with ViMiC, and surround sound, which will allows dynamic source movement, speaker positioning, and scalability. The advantage of using this hybrid approach is the application of WFS to home theater systems without facing the complexity of a complete two-dimensional WFS array, while still allowing for an immersive sound presentation. A psychoacoustic evaluation will be presented, as well as measurements of the composed sound field.

On the evolution of controllers for sound spatialization

Dynamic changes in spatial sound attributes have played a role in classical Western music for a long time. It is known that choreographic movements of opera singers were sometimes made for acoustic considerations. Probably the first mechanical spatial sound controller is the so-called wind swell that is found in pipe organs. Already in 1712, Renatus Harris mentions how swelling enables the player to project the sound of the pipes ad libitum to nearby or further distances. With the invention of electroacoustic music, a number of electromechanical devices were developed to control spatial aspects of sound (primarily positioning sound sources in 3-D space). Typical examples are Stockhausen’s rotational table (developed in the 1950s) and Manfred Krause’s sound mill (1960). In this presentation, the evolutionary steps in the design of spatial sound controllers will be outlined—beginning with early, purely mechanical devices up to recent approaches including the author’s participation in the development of a gestural controllable sound system based on virtual microphone control (ViMiC).

Simulating the acoustics of classical sound recording techniques in rooms

Recently, a method to position sound sources in 3-D space using virtual microphone control has been proposed [J. Acoust. Soc. Am. 117, 2391]. In this computer-generated environment, gains and delays between a virtual sound source and virtual microphones are calculated according to their distances and the axis orientations of the microphone directivity patterns. In the follow-up study reported here, it was investigated how to best simulate the influence of a room on the virtual microphone recording. For this purpose, a virtual rectangular room was created using the mirror-image technique (up to second-order reflections). The room dimensions were copied from an existing concert space at McGill University. Late reverb was created using a multiple feedback delay network with a time-variant architecture to enable modulation. To evaluate the system, measured impulse responses between a sound source and a five-channel microphone setup were compared to the virtual impulse responses for the same room/microphone-placement configuration. Among the tested parameters was the signal ratio between direct sound source and reflections as a function of the microphone placement and choice of microphone directivity patterns. The coherence between the simulated microphone signals was adjusted as well from the measured data. [Work supported by NSERC and VRQ.]