In DVD focus servo system, the skew of the disc induces periodic disturbance whose frequency is the same with the rotation frequency of the disc.

在DVD聚焦伺服系统中，光盘翘曲会导致产生与光盘转动频率相同的周期性扰动。

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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.

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。

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The first part is about the features extraction, including the estimation of source level of the ship-radiated noise and the line extraction of the rotation frequency of propeller noise spectrum.

首先是舰船辐射噪声特征量的提取，包括舰船总声源级的估计和螺旋桨轴频线谱的提取。

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"If the sudden frequency change is neglected, then after only eight hours, a complete rotation of the pulsar is lost in our counting, and we can no longer determine at which rotational phase the gamma-ray photons reach the detector aboard Fermi, " Pletsch explained.

MSN: Oddball pulsating star hiccups as it spins