Speech Enhancement by Multichannel Crosstalk Resistant ANC and Improved Spectrum Subtraction
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Speech Enhancement by Multichannel Crosstalk Resistant ANC and Improved Spectrum Subtraction Qingning Zeng and Waleed H. Abdulla Department of Electrical and Computer Engineering, The University of Auckland, Private Bag 92019, Auckland, New Zealand Received 31 December 2005; Revised 3 August 2006; Accepted 13 August 2006 A scheme combining multichannel crosstalk resistant adaptive noise cancellation (MCRANC) algorithm and improved spectrum subtraction (ISS) algorithm is presented to enhance noise carrying speech signals. The scheme would permit locating the microphones in close proximity by virtue of using MCRANC which has the capability of removing the crosstalk effect. MCRANC would also permit canceling out nonstationary noise and making the residual noise more stationary for further treatment by ISS algorithm. Experimental results have indicated that this scheme outperforms many commonly used techniques in the sense of SNR improvement and music effect reduction which is an inevitable byproduct of the spectrum subtraction algorithm. Copyright © 2006 Hindawi Publishing Corporation. All rights reserved.
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INTRODUCTION
Many speech enhancement algorithms have been developed in the previous years as speech enhancement is a core target in many demanding areas such as telecommunications, and speech and speaker recognitions. Among them, spectrum subtraction (SS) [1–3] and adaptive noise cancellation (ANC) [4] are the most practical and effective algorithms. SS algorithm needs only one channel signal and can be easily implemented with the existing digital hardware. It has been embedded in some high-quality mobile phones. Nevertheless, SS is only appropriate for stationary noise environments. Furthermore, it inevitably introduces “music noise” problem. In fact, the higher the noise is suppressed, the greater the distortion is brought to the speech signal and accordingly the poorer the intelligibility of the enhanced speech is obtained. As a result, ideal enhancement can hardly be achieved when SNR of the noisy speech is relatively low; below 5 dB. In contrast, it has quite good result when SNR of the noisy speech is relatively high; above 15 dB. On the other hand, ANC algorithm can be used to enhance speech signals in many noisy environments situations. However, it requires two channels to acquire signals for processing; the main channel and the referential channel. In addition, the referential channel signal should contain only noise signal. This implies that the referential microphone should be somewhat far from the main microphone. It has been proven that because of the propagation complexity of the audio signal in the practical environment, the farther the referential microphone from the main microphone, the
smaller the correlation of the referential signal with the main signal and accordingly less noise could be cancelled. Thus, the enhancement effect of ANC algorithm is in fact also quite limited. Fortunately, multichannel version of ANC algorithm can increase the cancellation effect since two or more referential signa
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