An integrated MVDR beamformer for speech enhancement using a local microphone array and external microphones

Randall Ali,Marc Moonen,Toon Van Waterschoot

doi:10.1186/s13636-020-00192-2

Randall Ali, Marc Moonen + Show 1 more

Open Access

https://doi.org/10.1186/s13636-020-00192-2

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Abstract

An integrated version of the minimum variance distortionless response (MVDR) beamformer for speech enhancement using a microphone array has been recently developed, which merges the benefits of imposing constraints defined from both a relative transfer function (RTF) vector based on a priori knowledge and an RTF vector based on a data-dependent estimate. In this paper, the integrated MVDR beamformer is extended for use with a microphone configuration where a microphone array, local to a speech processing device, has access to the signals from multiple external microphones (XMs) randomly located in the acoustic environment. The integrated MVDR beamformer is reformulated as a quadratically constrained quadratic program (QCQP) with two constraints, one of which is related to the maximum tolerable speech distortion for the imposition of the a priori RTF vector and the other related to the maximum tolerable speech distortion for the imposition of the data-dependent RTF vector. An analysis of how these maximum tolerable speech distortions affect the behaviour of the QCQP is presented, followed by the discussion of a general tuning framework. The integrated MVDR beamformer is then evaluated with audio recordings from behind-the-ear hearing aid microphones and three XMs for a single desired speech source in a noisy environment. In comparison to relying solely on an a priori RTF vector or a data-dependent RTF vector, the results demonstrate that the integrated MVDR beamformer can be tuned to yield different enhanced speech signals, which may be more suitable for improving speech intelligibility despite changes in the desired speech source position and imperfectly estimated spatial correlation matrices.

Highlights

Speech processing devices such as a hearing aid, a cochlear implant, or a mobile telephone are commonly equipped with an array of microphones to capture the acoustic environment
The integrated minimum variance distortionless response (MVDR) beamformer is reformulated from an alternative perspective, namely that of a quadratically constrained quadratic program (QCQP). This QCQP will consist of two constraints, one of which is related to the maximum tolerable speech distortion for the imposition of the a priori relative transfer function (RTF) vector and the other related to the maximum tolerable speech distortion for the imposition of the data-dependent RTF vector
7 Conclusion An integrated MVDR beamformer that merges the benefits from using an available a priori relative transfer function (RTF) vector and a data-dependent RTF vector was developed for a microphone configuration consisting of a local microphone array (LMA) and multiple external microphones (XMs)

Summary

Introduction

Speech processing devices such as a hearing aid, a cochlear implant, or a mobile telephone are commonly equipped with an array of microphones to capture the acoustic environment. An integrated MVDR beamformer for a microphone configuration with an LMA and XMs will merge an a priori RTF vector that is based on partial a priori knowledge and a fully data-dependent one. The additional insight of the QCQP formulation is that these tuning parameters or Lagrangian multipliers can be related to a maximum tolerable speech distortion for the imposition of the a priori or the data-dependent RTF vector An analysis of this relationship is provided, which facilitates the tuning of the integrated MVDR beamformer from the more intuitive perspective of the maximum tolerable speech distortions as opposed to the combination of filters as in [22].

Unprocessed signals

Integrated MVDR beamformer

Confidence metric and tuning

Beam patterns for a linear microphone array

Conclusion