说明：  小波变换的一级分解过程是，原始信号分别进行低通、高通滤波，再分别进行二元下抽样，就得到低频、高频（也称为平均、细节）两部分系数；而多级分解则是对上一级分解得到的低频系数再进行小波分解，是一个递归过程。
(Wavelet decomposition level is, the original signal were low-pass, high pass filter, and then carried out under the binary sample, we obtained low-frequency, high-frequency (also known as the average, details) coefficient of two parts and multi-level decomposition it is the decomposition level to be low-frequency coefficients further wavelet decomposition is a recursive process.)