An Integrated Real-Time Beamforming and Postfiltering System for Nonstationary Noise Environments
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An Integrated Real-Time Beamforming and Postfiltering System for Nonstationary Noise Environments Israel Cohen Department of Electrical Engineering, Technion – Israel Institute of Technology, Haifa 32000, Israel Email: [email protected]
Sharon Gannot School of Engineering, Bar-Ilan University, Ramat-Gan 52900, Israel Email: [email protected]
Baruch Berdugo Lamar Signal Processing, Ltd., Andrea Electronics Corp., P.O. Box 573, Yokneam Ilit 20692, Israel Email: [email protected] Received 1 September 2002 and in revised form 6 March 2003 We present a novel approach for real-time multichannel speech enhancement in environments of nonstationary noise and timevarying acoustical transfer functions (ATFs). The proposed system integrates adaptive beamforming, ATF identification, soft signal detection, and multichannel postfiltering. The noise canceller branch of the beamformer and the ATF identification are adaptively updated online, based on hypothesis test results. The noise canceller is updated only during stationary noise frames, and the ATF identification is carried out only when desired source components have been detected. The hypothesis testing is based on the nonstationarity of the signals and the transient power ratio between the beamformer primary output and its reference noise signals. Following the beamforming and the hypothesis testing, estimates for the signal presence probability and for the noise power spectral density are derived. Subsequently, an optimal spectral gain function that minimizes the mean square error of the log-spectral amplitude (LSA) is applied. Experimental results demonstrate the usefulness of the proposed system in nonstationary noise environments. Keywords and phrases: array signal processing, signal detection, acoustic noise measurement, speech enhancement, spectral analysis, adaptive signal processing.
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INTRODUCTION
Postfiltering methods for multimicrophone speech enhancement algorithms have recently attracted an increased interest. It is well known that beamforming methods yield a significant improvement in speech quality [1]. However, when the noise field is spatially incoherent or diffuse, the noise reduction is insufficient and additional postfiltering is normally required [2]. Most multimicrophone speech enhancement methods comprise a multichannel part (either delaysum beamformer or generalized sidelobe canceller (GSC) [3]) followed by a postfilter, which is based on Wiener filtering (sometimes in conjunction with spectral subtraction). Numerous articles have been published on that subject, for example, [4, 5, 6, 7, 8, 9, 10, 11, 12] to mention just a few. A major drawback of these multichannel postfiltering techniques is that highly nonstationary noise components are not dealt with. The time variation of the interfering signals is
assumed to be sufficiently slow such that the postfilter can track and adapt to the changes in the noise statistics. Unfortunately, transient interferences are often much too brief and abrupt for the conventional tracking methods.
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