提取原始信号的功率谱就可以看出在哪个频带的能量比较高，噪声主要集中在哪里，这样就可以专门分析那个频带的噪声-The power extracted　the spectrum of the original signal can be seen in which frequency band energy is high, the noise is mainly concentrated in where, so that it can be devoted to the analysis of the frequency band of noise