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