Effects of time window on the estimation of coherence function for the system with delay

概要

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The effects of the shape of time window on the estimation of the coherence function for the system having group delay are investigated. It is well known that the time-windowing determines the spectral resolution and the sidelobes, and that the sitable time window should be selected from that point of view. Time-windowing has another effect on the estimation when the system has group delay. Since the cross power spectrum obtained from DFT's corresponds to the circular conbolution of the input and output sequences in time domain, the windowed input and output include the uncorrelated components in the initial and final parts of the windows due to group delay. Consequently, the estimation of the coherence function is biased toward zero. The estimation is improved by using the Hanning window as far as the delay is sufficiently shorter than the window duration, but the rectanglar window becomes superior to the Hanning window when the delay is longer than about 0. 18 times of the window duration. Theoritical and experimental results indecate the effect of time window on the estmation of the coherence function .
社団法人日本音響学会の論文