Parametric virtual microphone techniques for sound field reconstruction with early reflection modeling

Aiming at the problem of sound field online monitoring and reconstruction inside the cabin, an inner acoustic field reconstruction method based on the optimal arrangement of sound monitoring points near the surface in the cabin is proposed. First, the method determines the truncation order of the acoustic cavity mode based on the analysis frequency range and calculates the sound pressure of each acoustic cavity mode at alternative locations near the inner surface of the cabin acoustic monitoring point. Second, the modal confidence matrix is used as the objective function, and the position of acoustic monitoring points is optimized via quantum particle swarm optimization (QPSO). Finally, the sound field near the interior surface of the cabin is reconstructed based on the optimal arrangement of sound monitoring points, and then the equivalent source method is used to reconstruct the sound field at any position in the cabin. In this paper, the sound field reconstruction accuracy in the cabin is analyzed using the proposed method and the traditional equivalent source method. Besides, the optimum performance of different optimization algorithms is compared. The results show that the proposed method is more accurate than the traditional equivalent source method when the number of monitoring points is the same, and the QPSO algorithm shows the best monitoring point location optimization performance. The effectiveness of the proposed method is further verified by cabin model experiment. Simulation and test results show that the accuracy of acoustic field reconstruction in the cabin based on the proposed method is less than 3 dB in the frequency band below 500 Hz.

The process of capturing, analyzing and predicting sound fields is finding novel areas of applications in AR/VR. One of the key processes in such applications is to estimate the sound field at locations that differ from the actual measurement points—i.e., the sound field reconstruction. However, it's a difficult spatial audio processing problem. Though theoretical solutions exist to reconstruct sound fields, they are practically infeasible due to hardware and computational requirements. This paper discusses the implementation of a system for large area sound field recording and reconstruction and proposes an improved sound field reconstruction algorithm. The proposed algorithm introduces a practical improvement in order to overcome implementation issues. In addition, we present a preliminary real-world results on an innovative but highly challenging application.

The acousto-optic effect can be used to measure the pressure fluctuations in air created by acoustic disturbances (the propagation of light is affected by changes in the medium due to the presence of sound waves). This makes it possible to measure an arbitrary sound field using acousto-optic tomography via scanning the field with a laser Doppler vibrometer. Consequently, the spatial characteristics of the sound field are captured in the measurement, implicitly bearing the potential for a full holographic reconstruction in a three-dimensional space. Recent studies have examined the reconstruction of sound pressure fields from acousto-optic measurements in the audible frequency range, based on Fourier transforms and elementary wave expansion methods. The present study examines the complete reconstruction of the sound field from acousto-optic measurements, recovering all acoustic quantities, and compares the results to the ones obtained from conventional microphone array measurements.

An enhancement to sound field reconstruction is proposed which improves subjective spatial perception and widens the sweet spot size of a 5 channel surround system. With the popularization of multi-channel audio systems, consumers have access to artificially generated surround sound found in movie audio tracks in addition to recordings featuring the preservation of the original audio space. How to achieve the latter is of question. A recording technique for perceptual sound field reconstruction(PSR) has been proposed by Jim Johnston et al., at AT&T. We now present an enhancement to PSR that can be applied to other surround sound systems. With most commercial surround sound reproduction, sound is directly radiated from all loudspeakers whether the original signal is direct or diffuse/reverberant. In contrast to an attack, reverberation is a far-field multipath phenomenon and reaches the ear as a sequence of decaying reflections. It is therefore desirable to reproduce recordings by scattering the diffuse field as well as radiating the direct field. In the proposed system, the direct field is radiated with a conventional loudspeaker while the diffuse sound field is separated and radiated with a loudspeaker/diffusor combination. The presented design utilizes the ear's ability to localize sound sources while preserving the perceptual spaciousness of the sound field. A digital switch was implemented to split the fields for each direct/diffuse loudspeaker pair.

To investigate the feasibility of low-concentration contrast media (LC-CM) in cerebral and cervical dual-energy CT angiography (DE-CTA) using an advanced monoenergetic (Mono+) reconstruction technique. Sixty-five consecutive patients prospectively selected to undergo cerebral and cervical DE-CTA were randomised into two groups: 32 patients (63.7 ± 9.7 years) in the high-concentration contrast medium (HC-CM) group with iopromide 370 and 33 patients (60.7 ± 10.8 years) in the low-concentration contrast medium (LC-CM) group with iodixanol 270. Traditional monoenergetic (Mono) and Mono+ images from 40 to 100 keV levels (at 10-keV intervals) and the standard mixed (Mixed, 120 kVp equivalent) images were reconstructed. Subjective image quality parameters included the contrast-to-noise ratio (CNR) and objective image quality parameters were evaluated and compared between the two groups. The 40-keV Mono+ images in the LC-CM group showed comparable objective CNR (common carotid arteries: 83.7 ± 24.5 vs. 78.1 ± 23.2; internal carotid arteries: 82.2 ± 26.8 vs. 76.8 ± 24.1; middle cerebral arteries: 72.5 ± 24.6 vs. 70.6 ± 19.2; all p > 0.05) and subjective image scores (3.95 ± 0.19 vs. 3.83 ± 0.35; p > 0.05) compared with Mixed images in the HC-CM group. The Mono+ reconstruction technique could reduce the concentration of iodinated CM in the diagnosis of cerebral and cervical angiography. • Mono+ shows decreased noise and superior CNR compared with Mono. • The 40-keV Mono+ images show the highest CNR in the LC-CM group. • The Mono+ reconstruction technique could reduce the concentration of iodinated CM.

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.

Characterising acoustic fields in rooms is challenging due to the complexity of data acquisition. Sound field reconstruction methods aim at predicting the acoustic quantities at positions where no data are available, incorporating generalisable physical priors of the sound in a room. This study introduces a model that exploits the general time structure of the room impulse response, where a wave-based expansion addresses the direct sound and early reflections, localising their apparent origin, and kernel methods are applied to the late part. This late energy is considered to follow a sinc-like spatial correlation, in accordance with the random wave field theory. Synthesised pressure points, which follow the observed statistics of the sound field, are introduced to enable extrapolation over large distances. The model is evaluated experimentally in a lecture room and an auditorium, demonstrating a successful reconstruction of the sound field across a 5 m aperture using three microphone arrays of only 4.2 cm radius each. These results indicate that the proposed methodology enables volumetric extrapolation over several orders of magnitude, which is significant in the context of navigable sound field reproduction, "6-degrees of freedom" spatial audio and sound field analysis in rooms.

In order to overcome the obstacle of singular integral in boundary element method (BEM), we presented an efficient sound field reconstruction technique based on the wave superposition method (WSM). Its principle includes three steps: first, the sound pressure field of an arbitrary shaped radiator is measured with a microphone array; then, the exterior sound field of the radiator is computed backward and forward using the WSM; at last, the final results are visualized in terms of sound pressure contours or animations. With these visualized contours or animations, noise sources can be easily located and quantified; also noise transmission path can be found out. By numerical simulation and experimental results, we proved that the technique are suitable and accurate for sound field reconstruction. In addition, we presented a sound field reconstruction system prototype on the basis of this technique. It makes a foundation for the application of wave superposition in the sound field reconstruction in industry situations.

We previously proposed the virtual microphone technique to improve the speech enhancement performance in underdetermined situations, in which the number of channels is virtually increased by estimating extra observed signals at arbitrary positions along the straight line formed by real microphones. In our previous work, the effectiveness of the interpolation of virtual microphone signals for speech enhancement was experimentally confirmed. In this study, to examine the effectiveness of the extrapolation of a virtual microphone in improving the speech enhancement performance, we apply this technique to speech enhancement using a maximum signal-to-noise ratio (SNR) beamformer. Next, to improve the speech enhancement performance on the basis of the virtual microphone technique, we propose a new arrangement where a virtual microphone is placed in a position proportional to the wavelength. From the results of an experiment in an underdetermined situation, we confirmed that the proposed method markedly improves speech enhancement performance. Moreover, we present directivity patterns to confirm the behavior of each method of positioning the virtual microphone.

The high-spatial-resolution nature of optical non-invasive measurement and the reconstruction of three-dimensional sound fields are important for evaluating acoustic transducers. The computed tomography (CT) method has been used to reconstruct sound fields from optical measurement results because of its contactless feature. However, since the CT method does not assume any physical property of sound, it may not be suitable for the reconstruction of sound fields. In contrast, a physical-model-based method is able to reconstruct sound fields more accurately by considering the physics of sound. In this study, we propose a scan-free and physical-model-based reconstruction of a three-dimensional sound field. A sound field is multi-directionally measured using parallel phase-shifting interferometry and a high-speed polarization camera by rotating an acoustic transducer. A physical-model-based method is applied to reconstruct the sound field from the recorded optical interferograms. We also discussed the effectiveness of the proposed method to evaluate acoustic transducers.

An application of active noise control (ANC) is the active headrest, using actuators (loadspeakers), sensors (microphones), and a controller to create a local zone of quiet around the occupants head. In this paper, the attenuation performance of various ANC-algorithms for active headrests known from literature is evaluated considering non-stationary broadband disturbances and head movement. Numerical studies are performed to determine the optimal plant models and parameters for the ANC-algorithms. Based on the findings of the numerical studies, several real-time experiments are conducted with and without head tracking examining the distribution of the 10 dB zone of quiet and the attenuation at the occupants ear using either a head mounted microphone technique, the remote microphone technique, the virtual microphone technique, or the virtual microphone control method. It is found that none of the algorithms using a virtual sensing technique can produce a 10 dB zone of quiet for all considered non-stationary broadband disturbances and head movement. For the algorithm using a head mounted microphone, it is possible to form a 10 dB zone of quiet, but placing a microphone at the ear is not feasible in most situations.

Spatial sound acquisition aims at capturing the sound field such that spatial cues present in the sound scene at the recording side are preserved at the reproduction side. The virtual microphone technique is a spatial recording method that allows for an arbitrary selection of the recording position and orientation. It exploits the parametric information about the sound field estimated using distributed microphone arrays in order to synthesize the virtual microphone signals that sound perceptually similar to the signals that would be recorded using physical microphones located at the same positions. In this paper, the quality of the spatial image in virtual stereo recordings is evaluated through a set of subjective experiments, including dedicated tests for distance and angle perception. The listening test results show that the spatial image captured using virtual microphones is perceptually close to the image recorded with physical microphones positioned analogously.

Holographic techniques are used to detect noise sources in a wide range of devices. Some of these techniques are commonly employed in the reconstruction of sound fields produced by automobile or motorcycle engines. These sound fields are characterized by having several, rather than single, temperatures; in fact, temperature gradients are frequently found in regions near the engine. These gradients produce changes in every point of the sound wave velocity. The mathematical model presented in this paper was designed to minimize the effect of assuming a constant sound velocity in the entire space in reconstruction of the sound field. It is based on the space transformation of sound field (STSF) technique [Hald, Jo/rgen, B&K Tech. Rev. 1, 1–50 (1989)], which uses a microphone array to measure pressure or determine the principal component of cross spectra over a hologram plane. The model scans the sound field in two planes. The first plane is used as an STSF initial condition (hologram plane), and the second plane is considered the boundary condition to Rayleigh integral’s propagation.

Virtual planning of open cranial vault reconstruction is used to simulate and define an pre-operative plan for craniosynostosis surgery. However, virtual planning techniques are subjective and dependent on the experience and preferences of the surgical team. To develop an objective automated 3D pre-operative planning technique for open cranial vault reconstructions, we used curvature maps for the shape comparison of the patient’s skull with an age-specific reference skull. We created an average skull for the age-group of 11–14 months. Also, we created an artificial test object and selected a cranial CT-scan of an 11 months old trigonocephaly patient as test case. Mesh data of skulls were created using marching cubes and raycasting. Curvature maps were computed using quadric surface fitting. The shape comparison was tested for the test object and the average skull. Finally, shape comparison was performed for the trigonocephalic skull with the average skull. Similar shapes and the area on the patient’s skull that maximally corresponded in shape with the reference shape were correctly identified. This study showed that curvature maps allow the comparison of craniosynostosis skulls with age-appropriate average skulls and a first step towards an objective user-independent pre-operative planning technique for open cranial vault reconstructions is made.

The sound quality of the vehicle interior response and fuel efficiency are two important considerations that influence customer purchase decision. However, these two objectives often have opposing design requirements. The reason is because a more fuel efficient vehicle generally requires lower overall weight. On the other hand, to achieve a quieter vehicle with premium sound quality inside the passenger compartment using traditional passive noise control strategy typically leads to a more massive body structure. In recent years, as a response to the need to further improve vehicle interior sound quality, a number of patents on active noise control (ANC) begin to appear. The proposed patented systems basically use a destructive sound wave form to treat the unwanted noise. This approach is gaining popularity as an alternative way to design a quieter car without the cost of weight penalty. This is made possible with recent rapid development of high performance signal processing software and hardware systems. The existing, patented active noise control systems are most effective for suppressing low frequency noise as compared to the traditional passive control applications. Even though the active vehicle noise control technology is not fully matured yet, the number of investigations and related patents in the open literature has risen over the years. Hence, there is merit to review the existing patents on active control of vehicle systems, and to provide a candid discussion on the direction and trend of this capability in the future. Keywords: Active noise control, active noise reduction, active noise suppression, acoustic noise tuning, vehicle noise control, vehicle interior response, fuel efficiency, NVH, filtered-x least mean square, FxLMS, signal processing unit, internal model controller, IMC algorithm, adaptive filter, signal generator, limiting amplifier, abnormal acoustic noise, adaptive notch filters, finite impulse response, secondary path filter, filtered reference signal, sinusoidal waveform generator, Bluebird, virtual microphone arrangement, the remote microphone technique, feedforward difference prediction tech-nique, adaptive LMS virtual microphone technique, Kalman filtering virtual sensing method, stochastically optimal tonal diffuse field virtual sensing technique