David L. Alon

Direction of arrival estimation using pseudo-intensity vectors with direct-path dominance test

The accuracy of direction of arrival estimation tends to degrade under reverberant conditions due to the presence of reflected signal components which are correlated with the direct path. The recently proposed direct-path dominance test provides a means of identifying time-frequency regions in which a single signal path is dominant. By analysing only these regions it was shown that the accuracy of the FS-MUSIC algorithm could be significantly improved. However, for real-time implementation a less computationally demanding localisation algorithm would be preferable. In the present contribution we investigate the direct-path dominance test as a preprocessing step to pseudo-intensity vector-based localisation. A novel formulation of the pseudo-intensity vector is proposed which further exploits the direct path dominance test and leads to improved localisation performance.

Beamforming with optimal aliasing cancellation in spherical microphone arrays

Spherical microphone arrays facilitate three-dimensional processing and analysis of sound fields in applications such as music recording, beamforming and room acoustics. The frequency bandwidth of operation is constrained by the array configuration. At high frequencies, spatial aliasing leads to side-lobes in the array beam pattern, which limits array performance. Previous studies proposed increasing the number of microphones or changing other characteristics of the array configuration to reduce the effect of aliasing. In this paper we present a method to design beamformers that overcome the effect of spatial aliasing by suppressing the undesired side-lobes through signal processing without physically modifying the configuration of the array. This is achieved by modeling the expected aliasing pattern in a maximum-directivity beamformer design, leading to a higher directivity index at frequencies previously considered to be out of the operating bandwidth, thereby extending the microphone array frequency range of operation. Aliasing cancellation is then extended to other beamformers. A simulation example with a 32-element spherical microphone array illustrates the performance of the proposed method. An experimental example validates the theoretical results in practice.

Spherical microphone array with optimal aliasing cancellation

Spherical microphone arrays facilitate spatial analysis of sound fields. At the high frequencies the array performance is limited by spatial aliasing. In this paper we present a method to extend the bandwidth of the array through optimal aliasing cancellation. The advantage and novelty of the proposed method is that aliasing cancellation is achieved through signal processing without physically modifying configuration of the spherical microphone array. In this work we show that by taking into account the expected aliasing pattern with respect to the given array sampling scheme, a beamformer which suppresses the grating-lobes can be designed. This beamformer achieves a higher directivity-index at frequencies previously considered as out of the microphone array operating range, therefore increasing the overall frequency range of operation. A simulation example with a 32 elements spherical microphone array illustrate the proposed method.

Robust plane-wave decomposition of spherical microphone array recordings for binaural sound reproduction

Rendering binaural signals from spherical microphone recordings is becoming an increasingly popular approach, with applications in telecommunications, virtual acoustics, hearing science, and entertainment. Such binaural signals can be generated from a plane-wave decomposition of a sound field measured by a spherical microphone array. This process may exhibit ill-conditioned transformations when performed at low frequencies and using high spherical-harmonics orders, thus resulting in a poor robustness to measurement inaccuracies and noise. Previous studies have addressed this issue by employing standard regularization techniques, such as diagonal loading and radial filter limiting. In this paper, we propose an optimal frequency-dependent regularization method that balances system robustness to measurement noise against accuracy of plane-wave decomposition. Unlike previously suggested approaches, the proposed method analytically relates the measured signal-to-noise ratio to the corresponding regularization ...

Spatial aliasing-cancellation for circular microphone arrays

Circular microphone arrays facilitate spatial processing and analysis of sound fields in applications where the sound field sources are primarily expected from the azimuthal directions. The operating frequency bandwidth of the array depends on the array aperture and on the number of microphones. At high frequencies, spatial aliasing generates side-lobes in the array beam pattern, which limits array performance. One way to reduce the spatial aliasing effect and to extend the array operating bandwidth is to increase the number of microphones. In this paper, a novel method for designing beam-formers that overcome the effect of spatial aliasing is presented. The undesired side-lobes are suppressed through signal processing without increasing the number of microphones or physically modifying the array. This is achieved by taking into account the expected aliasing pattern in the beamformer design, leading to a higher directivity-index at frequencies previously considered to be beyond the microphone array frequency range of operation. A simulation example with a 15-element circular microphone array illustrates the performance of the proposed method.

Efficient aliasing-free HRTF representation

Previous studies have shown that individualized head related transfer functions (HRTFs) provide improved localization performance compared to generic HRTF filters, and are therefore considered preferable for binaural sound reproduction. However, individualized HRTFs typically require a large number of measurements, which may extend to several hours. Therefore, they are currently unavailable for the vast majority of users. One approach to lower measurement complexity is to reduce the number of HRTF measurements. This approach although simplifies the measurement process, produces spatial aliasing leading to interpolation error away from the measured directions. In this study, a new method for the measurement of individualized HRTFs with a reduced spatial aliasing error is developed. The reduced spatial aliasing error is achieved by incorporating a small number of individualized HRTF measurements with information from a high resolution HRTFs database, which leads to an optimal interpolation process in the se...

Spatial perception in binaural reproduction with sparse head-related transfer function measurement grids

Growing interest in virtual reality has led to greater demand for immersive virtual audio systems. High fidelity spatial audio requires individualized head related transfer functions (HRTFs). Individualized HRTFs are, however, typically unavailable as they require specialized equipment and a large number of measurements. This motivates the development of a simpler more accessible HRTF estimation process. Previous work has demonstrated that spherical-harmonics (SH) can be used to reconstruct the HRTF from a smaller number of sample points, but this method has two known types of error: spatial aliasing and truncation error. Aliasing refer to loss of ability to represent high frequencies. Truncation error refer to the fact the SH representation will be order-limited which further limits spatial resolution. In this paper, the effect of sparse measurement grids on the reproduced binaural signal is studied by analyzing both types of errors. The expected effect of these errors on the perceived location, external...