对信号进行FFT，绘制出频率变化振幅，以及Nyquist频率之前随频率变化的振幅，进行谱分析，对归一化频率0~1进行分析。(The signal is FFT, the amplitude of frequency change is drawn, and the amplitude of the frequency changes with the frequency before the Nyquist frequency. The spectral analysis is carried