研究结果显示，在频率域内，面波衰减系数分布与群速度分布具有一定的相关性。
The correlation property between the distribution of attenuation factor and that of the group velocity is indicated, in this study.
而时域同步平均可以有效衰减与回转频率无关的干扰，提取与工作状态直接相关的周期信号。
Time domain synchronous averaging can reduce the signal not coherent to rotation frequency effectively, and extract the repetitive signals directly related to machine operation condition.
针对语句后部的变调和基音频率的衰减，采用改进的自相关函数计算方法增强快变基音周期的跟踪。
We adopt improved computation of autocorrelation function for the case of fo change in the end of sentences, and realize accurate tracking to rapidly changed pitch.
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