说明：  本程序为应用小波变换进行信号压缩。由于本程序涉及到了小波变换的函数，因此可能涉及到一些时频分析工具箱的函数。程序中应用db3小波进行3层分解，选用全局阈值进行阈值处理，即对各高频系数使用同一个阈值，进行阈值处理。
(This procedure for the application of wavelet transform for signal compression. Since this procedure involves the wavelet transform of the function, it may involve a number of time-frequency analysis function of the toolbox. Procedures for the application of layer 3 to db3 wavelet decomposition, selection of the overall threshold threshold treatment, that is, on the high-frequency coefficients using the same threshold, the threshold for treatment.)