Daniel Marquardt

Interaural coherence preservation in multi-channel wiener filtering-based noise reduction for binaural hearing aids

Besides noise reduction an important objective of binaural speech enhancement algorithms is the preservation of the binaural cues of all sound sources. To this end, an extension of the binaural multi-channel Wiener filter (MWF), namely the MWF-ITF, has been proposed, which aims to preserve the Interaural Transfer Function (ITF) of the noise sources. However, the MWF-ITF is well-suited only for directional noise sources but not for, e.g., spatially isotropic noise, whose spatial characteristics cannot be properly described by the ITF but rather by the Interaural Coherence (IC). Hence, another extension of the binaural MWF, namely the MWF-IC, has been recently proposed, which aims to preserve the IC of the noise component. Since for the MWF-IC a substantial tradeoff between noise reduction and IC preservation exists, in this paper we propose a perceptually constrained version of the MWF-IC, where the amount of IC preservation is controlled based on the IC discrimination ability of the human auditory system. In addition, a theoretical analysis of the binaural cue preservation capabilities of the binaural MWF and the MWF-ITF for spatially isotropic noise fields is provided. Several simulations in diffuse noise scenarios show that the perceptually constrained MWF-IC yields a controllable preservation of the IC without significantly degrading the output SNR compared to the binaural MWF and the MWF-ITF. Furthermore, contrary to the binaural MWF and MWF-ITF, the proposed algorithm retains the spatial separation between the output speech and noise components while the binaural cues of the speech component are only slightly distorted, such that the binaural hearing advantage for speech intelligibility can still be exploited.

Theoretical analysis of binaural transfer function MVDR beamformers with interference cue preservation constraints

The objective of binaural noise reduction algorithms is not only to selectively extract the desired speaker and to suppress interfering sources (e.g., competing speakers) and ambient background noise, but also to preserve the auditory impression of the complete acoustic scene. For directional sources this can be achieved by preserving the relative transfer function (RTF) which is defined as the ratio of the acoustical transfer functions relating the source and the two ears and corresponds to the binaural cues. In this paper, we theoretically analyze the performance of three algorithms that are based on the binaural minimum variance distortionless response (BMVDR) beamformer, and hence, process the desired source without distortion. The BMVDR beamformer preserves the binaural cues of the desired source but distorts the binaural cues of the interfering source. By adding an interference reduction (IR) constraint, the recently proposed BMVDR-IR beamformer is able to preserve the binaural cues of both the desired source and the interfering source. We further propose a novel algorithm for preserving the binaural cues of both the desired source and the interfering source by adding a constraint preserving the RTF of the interfering source, which will be referred to as the BMVDR-RTF beamformer. We analytically evaluate the performance in terms of binaural signal-to-interference-and-noise ratio (SINR), signal-to-interference ratio (SIR), and signal-to-noise ratio (SNR) of the three considered beamformers. It can be shown that the BMVDR-RTF beamformer outperforms the BMVDR-IR beamformer in terms of SINR and outperforms the BMVDR beamformer in terms of SIR. Among all beamformers which are distortionless with respect to the desired source and preserve the binaural cues of the interfering source, the newly proposed BMVDR-RTF beamformer is optimal in terms of SINR. Simulations using acoustic transfer functions measured on a binaural hearing aid validate our theoretical results.

Theoretical analysis of linearly constrained multi-channel wiener filtering algorithms for combined noise reduction and binaural cue preservation in binaural hearing aids

Besides noise reduction, an important objective of binaural speech enhancement algorithms is the preservation of the binaural cues of all sound sources. For the desired speech source and the interfering sources, e.g., competing speakers, this can be achieved by preserving their relative transfer functions (RTFs). It has been shown that the binaural multi-channel Wiener filter (MWF) preserves the RTF of the desired speech source, but typically distorts the RTF of the interfering sources. To this end, in this paper we propose two extensions of the binaural MWF, i.e., the binaural MWF with RTF preservation (MWF-RTF) aiming to preserve the RTF of the interfering source and the binaural MWF with interference rejection (MWF-IR) aiming to completely suppress the interfering source. Analytical expressions for the performance of the binaural MWF, MWF-RTF and MWF-IR in terms of noise reduction, speech distortion and binaural cue preservation are derived, showing that the proposed extensions yield a better performance in terms of the signal-to-interference ratio and preservation of the binaural cues of the directional interference, while the overall noise reduction performance is degraded compared to the binaural MWF. Simulation results using binaural behind-the-ear impulse responses measured in a reverberant environment validate the derived analytical expressions for the theoretically achievable performance of the binaural MWF, MWF-RTF, and MWF-IR, showing that the performance highly depends on the position of the interfering source and the number of microphones. Furthermore, the simulation results show that the MWF-RTF yields a very similar overall noise reduction performance as the binaural MWF, while preserving the binaural cues of both the speech and the interfering source.

Binaural cue preservation for hearing aids using multi-channel wiener filter with instantaneous ITF preservation

An important objective of binaural noise reduction algorithms is the preservation of the binaural cues. In this paper an extension of the Multi-channel Wiener filter with binaural cue preservation (MWF-ITF) is presented, where the average noise ITF preservation term is replaced by an instantaneous noise ITF preservation term. This framework in addition allows to impose perfect ITF preservation, leading to a hard-constraint formulation. Experimental results show that the proposed technique yields a better performance in preserving the binaural cues of both the noise component and the speech component compared to the MWF-ITF, without degrading the output SNR.

Comparing Binaural Pre-processing Strategies I: Instrumental Evaluation

In a collaborative research project, several monaural and binaural noise reduction algorithms have been comprehensively evaluated. In this article, eight selected noise reduction algorithms were assessed using instrumental measures, with a focus on the instrumental evaluation of speech intelligibility. Four distinct, reverberant scenarios were created to reflect everyday listening situations: a stationary speech-shaped noise, a multitalker babble noise, a single interfering talker, and a realistic cafeteria noise. Three instrumental measures were employed to assess predicted speech intelligibility and predicted sound quality: the intelligibility-weighted signal-to-noise ratio, the short-time objective intelligibility measure, and the perceptual evaluation of speech quality. The results show substantial improvements in predicted speech intelligibility as well as sound quality for the proposed algorithms. The evaluated coherence-based noise reduction algorithm was able to provide improvements in predicted audio signal quality. For the tested single-channel noise reduction algorithm, improvements in intelligibility-weighted signal-to-noise ratio were observed in all but the nonstationary cafeteria ambient noise scenario. Binaural minimum variance distortionless response beamforming algorithms performed particularly well in all noise scenarios.

Optimal binaural LCMV beamformers for combined noise reduction and binaural cue preservation

Besides noise reduction an important objective of binaural speech enhancement algorithms is the preservation of the binaural cues of both desired and undesired sound sources. Recently, the binaural Linearly Constrained Minimum Variance (BLCMV) beamformer has been proposed that aims to preserve the desired speech component and suppress the undesired directional interference component while preserving the binaural cues of both components. Since the performance of the BLCMV beamformer highly depends on the amount of interference rejection determined by the interference rejection parameter, in this paper we propose several performance criteria to optimize the interference rejection parameters for the left and the right hearing aid. Experimental results show how the performance of the BLCMV beamformer is affected by the different optimal parameter combinations.

Coherence preservation in multi-channel Wiener filtering based noise reduction for binaural hearing aids

Besides noise reduction an important objective of binaural speech enhancement algorithms is the preservation of the binaural cues of both desired and undesired sound sources. Recently, an extension of the binaural Multi-channel Wiener filter (MWF), namely the MWF-IC, has been presented, which aims to preserve the Interaural Coherence (IC) of the noise component. Since for the MWF-IC a substantial trade-off between noise reduction and IC preservation exists, in this paper we propose a perceptually constrained version of the MWF-IC, where the amount of IC preservation is controlled based on psychoacoustic criterias of the IC discrimination ability of the human auditory system. In addition, we present a simplified version of the MWF-IC, resulting in a decrease of computational complexity. Experimental results show that the perceptually motivated MWF-IC and its simplified version yield a very similar performance and the loss in intelligibility weighted output SNR compared to the binaural MWF can be limited to 0.5 dB, whereas the spatial separation between the output speech and noise component is increased leading to better perceptual results.

Perceptually motivated coherence preservation in multi-channel wiener filtering based noise reduction for binaural hearing aids

Besides noise reduction an important objective of binaural speech enhancement algorithms is the preservation of the binaural cues of both desired and undesired sound sources. Recently, an extension of the binaural Multi-channel Wiener filter (MWF), namely the MWFIC, has been presented, which aims to preserve the Interaural Coherence (IC) of the noise component. Since for the MWF-IC a substantial trade-off between noise reduction and IC preservation exists, in this paper we propose a perceptually constrained version of the MWF-IC, where the amount of IC preservation is controlled based on psychoacoustic criterias of the IC discrimination ability of the human auditory system. In addition, we present a simplified version of the MWF-IC, resulting in a decrease of computational complexity. Experimental results show that the perceptually motivated MWF-IC and its simplified version yield a very similar performance and the loss in intelligibility weighted output SNR compared to the binaural MWF can be limited to 0.5 dB, whereas the spatial separation between the output speech and noise component is increased leading to better perceptual results.

Speech enhancement for multimicrophone binaural hearing aids aiming to preserve the spatial auditory scene

Modern binaural hearing aids utilize multimicrophone speech enhancement algorithms to enhance signals in terms of signal-to-noise ratio, but they may distort the interaural cues that allow the user to localize sources, in particular, suppressed interfering sources or background noise. In this paper, we present a novel algorithm that enhances the target signal while aiming to maintain the correct spatial rendering of both the target signal as well as the background noise. We use a bimodal approach, where a signal-to-noise ratio (SNR) estimator controls a binary decision mask, switching between the output signals of a binaural minimum variance distortionless response (MVDR) beamformer and scaled reference microphone signals. We show that the proposed selective binaural beamformer (SBB) can enhance the target signal while maintaining the overall spatial rendering of the acoustic scene.

Binaural multichannel Wiener filter with directional interference rejection

In this paper we consider an acoustic scenario with a desired source and a directional interference picked up by hearing devices in a noisy and reverberant environment. We present an extension of the binaural multichannel Wiener filter (BMWF), by adding an interference rejection constraint to its cost function, in order to combine the advantages of spatial and spectral filtering while mitigating directional interferences. We prove that this algorithm can be decomposed into the binaural linearly constrained minimum variance (BLCMV) algorithm followed by a single channel Wiener post-filter. The proposed algorithm yields improved interference rejection capabilities, as compared with the BMWF. Moreover, by utilizing the spectral information on the sources, it is demonstrating better SNR measures, as compared with the BLCMV.