An eight-channel database of head-related impulse responses (HRIRs) and binaural room impulse responses (BRIRs) is introduced. The impulse responses (IRs) were measured with three-channel behind-the-ear (BTEs) hearing aids and an in-ear microphone at both ears of a human head and torso simulator. The database aims at providing a tool for the evaluation of multichannel hearing aid algorithms in hearing aid research. In addition to the HRIRs derived from measurements in an anechoic chamber, sets of BRIRs for multiple, realistic head and sound-source positions in four natural environments reflecting dailylife communication situations with different reverberation times are provided. For comparison, analytically derived IRs for a rigid acoustic sphere were computed at the multichannel microphone positions of the BTEs and differences to real HRIRs were examined. The scenes' natural acoustic background was also recorded in each of the real-world environments for all eight channels. Overall, the present database allows for a realistic construction of simulated sound fields for hearing instrument research and, consequently, for a realistic evaluation of hearing instrument algorithms.
In this contribution different microphone array-based noise reduction schemes for hearing aids are suggested and compared in terms of their performance, signal quality and robustness against model errors. The algorithms all have binaural output and are evaluated using objective perceptual quality measures [1,2,3]. It has been shown earlier that these measures are able to predict subjective data that is relevant for the assessment of noise reduction algorithms. The quality measures showed clearly that fixed beamformers designed with head models were relatively robust against steering errors whereas for the adaptive beamformers tested in this study the robustness was limited and the benefit due to higher noise reduction depended on the noise scenario and the reliability of a direction of arrival estimation. Furthermore, binaural cue distortions introduced by the different binaural output strategies could be identified by the binaural speech intelligibility measure [3] even in case monaural quality values were similar. Thus, this perceptual quality measure seems to be suitable to discover the benefit that the listener might have from the effect of spatial unmasking.
In this study a self-steering beamformer with binaural output for a head-worn microphone array is investigated in simulated and realworld conditions. The influence of the underlying sound propagation model on the estimation accuracy of the direction of arrival (DOA) estimation algorithm and the overall performance of the combined DOA-beamformer-system is evaluated. For this, technical performance measures as well as objective quality measures based on perceptual models of the auditory system are used. The self-steering beamformer showed better performance than a beamformer with fixed look-direction for SNR values above -2 dB if the propagation model includes at least a coarse head model.
Multi-channel beamformer algorithms are promising solutions for noise reduction in hearing aids as they exploit the spatial distribution of the interfering signals and therefore in general lead to less signal distortion than single channel algorithms. Beamformers need a priori information about the microphone array and the direction of arrival of the target speech source. For head-worn arrays it is usually assumed that the user physically steers the arrays' look direction toward the desired speech source. This may become unsatisfying for the hearing aid user for high directivity beamformers with a small main lobe and when the target signal source is moving. In this contribution an automatic steering (electronic control of the look direction) is applied based on the dual delay line approach after Liu et al.. This approach is modified to be applicable for head-mounted hearing-aid arrays. We show that the original free-field approach does not work on a head-mounted array because of the inappropriate propagation model. If we apply the true HRTF or a spherical head propagation model, the estimate is reliable within plusmn8deg degree mean estimation error for an input SNR of 10 dB or higher. However, for lower SNR the method seems to be not robust enough
The performance of a fixed beamformer highly depends on the position of the microphones in the array. In this paper, different heuristic optimisation approaches for arbitrary planar arrays and an exhaustive search approach for structured array geometries are presented to optimise the microphone positions for a superdirective beamformer, aiming at maximizing the mean directivity index for several steering angles of interest. Through the derivation of an upper bound on the achievable performance, it is shown that the proposed approaches generate configurations with a near-optimal performance. In addition, the theoretical results are validated using real measurements, demonstrating the practical usability of the proposed methods
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