说明：  程序内容：使用sym4小波对信号进行一层小波分解，处理一层小波系数，并求处理后压缩信号与原信号的标准差
(Program content: The sym4 wavelet is used to decompose the signal by a layer of wavelet, and the wavelet coefficients are processed, and the standard deviation of the compressed signal and the original signal)