这里，主要对二次处理的方法作了详细的介绍，包括时域信号的统计特征，频域分析的傅立叶变换和短时傅立叶变换。

Here, secondary treatment methods are introduced in detail, include time domain signal statistics character, frequency analysis fast Fourier transform (FFT), and short time Fourier transform (STFT).

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本文首先对傅立叶变换的性质做了详细介绍，其中包括离散傅里叶变换，快速傅立叶变换（FFT）以及基-2按时间抽取（DIT）的FFT算法；

Firstly , the properties of Fourier Transform, including discrete Fourier Transform, FFT and based-2 DIT FFT, are introduced in this paper;

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