TEMPORAL SELECTIVE DEREVERBERATION OF NOISY SPEECH USING ONE MICROPHONE Emanu ¨ el A.P. Habets (2008)

Reverberant speech can be described as sounding distant with no- ticeable coloration and echo. These detrimental perceptual effects are caused by early and late reflections, respectively, and reduces the fidelity and intelligibility of speech. It is well-known that the echo density of the reflections increases with time. Therefore, the tempo- ral structure of early and late reflections differs. In this paper, we combine two different dereverberation techniques that were recently developed to suppress early and late reverberation separately. First, late reverberation is suppressed using a spectral processing tech- nique that is based on a statistical reverberation model. Secondly, early reverberation and residual late reverberation are suppressed us- ing a Linear Prediction (LP) residual processing technique. In addi- tion, an objective measure based on the kurtosis of the LP residual is proposed to measure the coloration caused by early reflections. Experimental results demonstrate the beneficial use of the new sin- gle microphone system that reduces echo and coloration with little speech distortion. a smaller number of (practically feasible) single-microphone speech dereverberation algorithms have been proposed, the development of novel single-microphone dereverberation algorithms continues to be an important research topic. Recently, a practically feasible single-microphone spectral pro- cessing technique has been developed that is able to suppress late reverberation and background noise (6). The algorithm is based on a statistical reverberation model which is characterized by the re- verberation time of the room and the Direct to Reverberation Ra- tio (DRR). In (5) a Spatiotemporal averaging Method for Enhance- ment of Reverberant Speech (SMERSH) has been developed which is based on processing of the residual signal following linear pre- diction. The speech signals are first spatially averaged followed by temporal averaging of the LP residual over adjacent larynx cycles of voiced speech. The effect of the inter-cycle averaging in the LP residual domain is embodied into an equalization filter which is sub- sequently applied to both voiced and unvoiced LP residual, and sup- presses the effects of early and late reflections. In this paper we develop a single-microphone system which con- sists of two-stages. In the first stage the spectral processing tech- nique proposed in (6) is used to suppress late reverberation. In ad- dition, we show how background noise can be suppressed in this stage. In the second stage, a single-microphone version of SMERSH algorithm is used to suppress early reverberation and residual late re- verberation. The performance of the LP residual processing in the presence of background noise is analysed. Furthermore, we show that the kurtosis of the LP residual signal is highly correlated with the standard deviation of the log amplitude spectrum of the RIR, which is a channel-based objective measure for the colouration in- troduced by the RIR. Using the kurtosis measure we are able to show that the LP residual processing can be used to reduce the colouration caused by the early reflections. This also confirms the study in (3, 4) where an adaptive filter maximizing the kurtosis of the LP residual was used to suppress early reverberation. The outline of the paper is as follows. In Section 2 the spectral and LP residual processing techniques are reviewed. In Section 3 the system containing the two dereverberation stages is discussed. Ex- perimental results, for different source-microphone and reverbera- tion times, are described in Section 4. Finally, conclusions are drawn in Section 5.