Abstract
This paper investigates the problem of enhancing a single desired speech source from a mixture of signals in multispeaker environments. A beamformer structure is proposed which combines a fixed beamformer with postfiltering. In the first stage, the fixed multiobjective optimal beamformer is designed to spatially extract the desired source by suppressing all other undesired sources. In the second stage, a multichannel power spectral estimator is proposed and incorporated in the postfilter, thus enabling further suppression capability. The combined scheme exploits both spatial and spectral characteristics of the signals. Two new multichannel spectral estimation methods are proposed for the postfiltering using, respectively, inner product and joint diagonalization. Evaluations using recordings from a real-room environment show that the proposed beamformer offers a good interference suppression level whilst maintaining a low-distortion level of the desired source.
Highlights
Multichannel beamforming techniques can be largely divided into three types, namely, fixed, optimum, and adaptive beamforming [1, 2]
The weights are calculated based on information about the array geometry and the source localization with no statistical information about the signal’s environment or the required signals
The beamformer coefficients are optimized in such a manner that a focussed beam is steered to a desired source direction, whilst suppressing the contributions coming from other directions [2, 3]
Summary
Multichannel beamforming techniques can be largely divided into three types, namely, fixed, optimum, and adaptive beamforming [1, 2]. The adaptive postfiltering uses the estimation of spectral densities of the desired and undesired signals in the filter output to further suppress the noise. One common method to perform postfiltering is spectral subtraction This method exploits spectral information of the noise and the speech sources to form a gain function to suppress the noise [8, 9]. A new beamformer structure is proposed which employs a multichannel power spectral estimator of the desired speech source. This structure includes a multiobjective optimal beamformer followed by a postfilter. To suppress further the undesired sources from the beamformer output, an adaptive postfilter is proposed which includes a multichannel spectral estimation of the desired signal.
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