说明：  通过fir1设计FIR滤波器，fir2设计任意频率响应的滤波器，采用卷积计算信号通过系统后响应（还原），采用fftfilt计算信号通过系统后响应，一个长序列和一个短序列的卷积。
(Fir1 through FIR filter design, fir2 design the frequency response of any filter, the use of convolution calculation of the signal through the system to respond to (restore), calculated using fftfilt signal through the system to respond to, a long sequence and a short sequence of convolution.)