说明：  滤波器的设计，包含低通滤波器，高通滤波器和带通滤波器，mtsg文件生成三个信号，分别对应低频，高频和中频，通过绘图看出滤波器的滤波效果
(The design of the filter includes low-pass filter, high-pass filter and band-pass filter. The MTSG file generates three signals, corresponding to low frequency, high frequency and medium frequency respectively. The filtering effect of the filter can be seen by drawing)