| 1. |
- Ahrens, Jens, 1978, et al.
(författare)
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A Head-Mounted Microphone Array for Binaural Rendering
- 2021
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Ingår i: 2021 Immersive and 3D Audio: From Architecture to Automotive, I3DA 2021.
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Konferensbidrag (refereegranskat)abstract
- We recently presented a method for obtaining a spherical harmonic representation of a sound field based on microphones along the equator of a rigid spherical object that ideally has a size similar to that of a human head. We refer to this setup as an equatorial microphone array. Even more recently, we presented an extension of this method that allows for employing a scattering object that is approximately spherical such as a human head. The present paper provides an overview as well as a juxtaposition of the two solutions. We present an instrumental evaluation based on the application of binaural rendering of the captured sound fields by analysing simulated binaural transfer functions of both methods for a variety of scenarios.
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| 2. |
- Ahrens, Jens, 1978
(författare)
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A Software Tool For Auralization of Simulated Sound Fields
- 2023
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Ingår i: Proceedings of the Institute of Acoustics. - 1478-6095. ; 45
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Konferensbidrag (refereegranskat)abstract
- We demonstrated an implementation of a set of methods for auralization of simulated sound fields. For the chosen grids of head size and of 343 pressure points or 100 or 150 sampling points for both pressure and pressure gradient, respectively, the binaural output signals of the methods deviate from the ground truth only at high frequencies and mostly on the contralateral side, which makes the output perceptually very similar to the ground truth. What combination of grid type, grid dimensions, and number of sampling points produces perceptually transparent auralization (i.e. an auralized signal that is perceptually indistinguishable from the ground truth) is unclear at this stage and is subject to further research. It is conceivable that such a combination can be found. The presented methods will then constitute a unified approach to auralization as they can be applied to any acoustical simulation method, be it wave-based, geometric, or energy-based, so long as the simulation method allows for computing volumetric sound pressure data. Simulation methods can thereby be compared perceptually without uncertainty regarding the influence of the auralization method on the result. © 2023 Institute of Acoustics. All rights reserved.
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| 3. |
- Ahrens, Jens, 1978
(författare)
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Amplitude Engineering for Beamformers with Self-Bending Directivity Based on Convex Optimization
- 2017
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Ingår i: IEEE Workshop on Applications of Signal Processing to Audio and Acoustics (WASPAA). - 9781538616314
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Konferensbidrag (refereegranskat)abstract
- Arrays producing self-bending beams were proposed in the literature recently. The self-bending property of the beam is achieved by matching the phase profile that is applied to the array elements to a self-bending wave field. This process is termed phase engineering. It has been unclear how the optimal amplitude profile can be determined as the amplitude distribution of a self-bending wave field is difficult to determine. Previous works employed educated guesses. In this paper, we apply convex optimization to perform amplitude engineering. In other words, we complement phase engineering by determining the purely real amplitude weights that minimize the norm of the amplitude weights for a given maximum beam amplitude in the dark zone around which the beam bends. We show that phase engineering by itself does not narrow down the solution space sufficiently so that the choice of control points in the dark zone has a significant impact on how well the desired self-bending property forms.
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| 4. |
- Ahrens, Jens, 1978, et al.
(författare)
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Auralization of acoustic spaces based on spherical microphone array recordings
- 2017
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Ingår i: Acoustics ’17, Boston, MA.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Microphone arrays can capture the physical structure of a sound field. They are therefore potentially suited to capture and preserve the sound of acoustic spaces within given physical limitations that are determined by the construction of the array. Especially spherical microphone arrays have received considerable attention in this context. Superposed onto the limitations of the microphone array are the limitations caused by the auralization system. We present results from user studies on the perceptual differences between spherical microphone array recordings that are auralized with headphones as well as with a circular 56-channel loudspeaker array and headphone auralization based on dummy head measurements of the same spaces. Head-tracking was applied in all cases in which headphones were used.
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| 5. |
- Ahrens, Jens, 1978
(författare)
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Auralization of Omnidirectional Room Impulse Responses Based on the Spatial Decomposition Method and Synthetic Spatial Data
- 2019
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Ingår i: ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings. - 1520-6149. ; , s. 146-150
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Konferensbidrag (refereegranskat)abstract
- The spatial decomposition method decomposes acoustic room impulse responses into a pressure signal and a direction of arrival for each time instant of the pressure signal. An acoustic space can be auralized by distributing the pressure signal over the available loudspeakers or head-related transfer functions so that the required instantaneous propagation direction is recreated. We present a user study that demonstrates based on binaural auralization that the arrival directions can be synthesized from random data such that the auralization is nearly indistinguishable from the auralization of the original data. The presented concept constitutes the fundament of a highly scalable spatialization method for omnidirectional room impulse responses.
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| 6. |
- Ahrens, Jens, 1978, et al.
(författare)
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Authentic Auralization of Acoustic Spaces Based on Spherical Microphone Array Recordings
- 2018
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Ingår i: Proceedings of the Institute of Acoustics. - 1478-6095. ; 40:3, s. 303-310
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Konferensbidrag (refereegranskat)abstract
- Many approaches for the capture and auralization of real acoustic spaces have been proposed over the past century. Limited spatial resolution on the capture side has typically been the factor that caused compromises in the achievable authenticity of the auralization. Recent advancements in the field of spherical microphone arrays provide new perspectives for both headphone-based and loudspeaker-based auralization. It has been shown that a bowling-ball-size spherical array of around 90 microphones allows for creating signals at the ears of the listener that are perceptually almost indistinguishable from the ear signals that arise in the original space. Head-tracked headphone auralization, i.e. playback that adapts to the instantaneous head orientation of the listener, has been shown to provide the best results. In the present contribution, we provide an overview of the technology and demonstrate the latest research advancements and remaining challenges.
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| 7. |
- Ahrens, Jens, 1978, et al.
(författare)
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Case Study of Equipping a High-Fidelity 360 Camera with a 4th-Order Equatorial Ambisonic Microphone Array
- 2023
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Ingår i: AES Europe 2023: 154th Audio Engineering Society Convention.
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Konferensbidrag (refereegranskat)abstract
- We present a case study of a commercial 360 camera that we equipped with an experimental 9-channel equatorial microphone array that uses the camera as the baffle and thereby becomes invisible for the video capture. The microphone array produces a 4th-order ambisonic audio recording that we render binaurally. The setup as a whole produces 360 audio-visual content that does not require any manual post-processing. The camera model that we chose has a perfectly circular horizontal cross-section, but its overall shape departs from a sphere. We demonstrate that approximating this baffle as a sphere in the signal processing causes negligible deviation of the resulting ear signals. The standard equatorial array processing approaches can therefore be employed, and costly calibration measurements are avoided. All resources are provided for download.
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| 8. |
- Ahrens, Jens, 1978, et al.
(författare)
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Computation of Spherical Harmonic Representations of Source Directivity Based on the Finite-Distance Signature
- 2021
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Ingår i: IEEE/ACM Transactions on Speech and Language Processing. - 2329-9290 .- 2329-9304. ; 29, s. 83-92
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Tidskriftsartikel (refereegranskat)abstract
- The measurement of directivity for sound sources that are not electroacoustic transducers is fundamentally limited because the source cannot be driven with arbitrary signals. A consequence is that directivity can only be measured at a sparse set of frequencies—for example, at the stable partial oscillations of a steady tone played by a musical instrument or from the human voice. This limitation prevents the data from being used in certain applications such as time-domain room acoustic simulations where the directivity needs to be available at all frequencies in the frequency range of interest. We demonstrate in this article that imposing the signature of the directivity that is obtained at a given distance on a spherical wave allows for all interpolation that is required for obtaining a complete spherical harmonic representation of the source’s directivity, i.e., a representation that is viable at any frequency, in any direction, and at any distance. Our approach is inspired by the far-field signature of exterior sound fields. It is not capable of incorporating the phase of the directivity directly. We argue based on directivity measurement data of musical instruments that the phase of such measurement data is too unreliable or too ambiguous to be useful. We incorporate numerically-derived directivity into the example application of finite difference time domain simulation of the acoustic field, which has not been possible previously.
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| 9. |
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| 10. |
- Ahrens, Jens, 1978, et al.
(författare)
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Evaluation of Non-Spherical Scattering Bodies for Ambisonic Microphone Arrays
- 2022
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Ingår i: Proceedings of the AES International Conference. ; 2022-August, s. 58-66
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Konferensbidrag (refereegranskat)abstract
- The XMA was recently presented, which is a higher-order ambisonic microphone array with a non-spherical scattering body. The approach is compatible with the also recently presented equatorial microphone array so that also XMAs can be designed with the microphones distributed solely on a circumferential contour around the scattering body. This greatly reduces the required number of microphones compared to classical spherical microphone arrays that require the microphones to be distributed over the entire surface of the scatterer. The equatorial XMA has so far only been evaluated as a head-mounted array, i.e. with a human head as the baffle. Other form factors of a range of sizes are also of practical relevance, particularly those form factors of 360 cameras as these are capable of capturing a complete panoramic audio-visual experience from a first-person view when combined with an equatorial XMA. We present a set of simulations based on which we identify what spherical harmonic orders can be obtained with what accuracy for a set of convex scattering body geometries that are of relevance in the given context. We demonstrate that the shape of the body is not very critical, and even corners are possible. The main limitation is that small bodies do not allow for extracting higher orders at low frequencies.
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