说明：  地震信号研究中，建立主频freq为15Hz的单道雷克子波，并进行频谱分析。这个是自己学习时编的，每步都有详细说明和个人认识。
(Study of seismic signals, the establishment of frequency freq 15Hz single-channel Ricker wavelet and spectral analysis. This learning series, each step in detail and personal understanding.)