FIR数字滤波器：里面包含四部分程序，分别对一个给定的信号进行低通滤波，高通滤波，带通滤波，带阻滤波（程序有详细的注释，适合新手学习FIR型数字滤波器）(FIR digital filter: which contains four parts of the program, respectively, for a given signal low-pass filter, high pass filter, band pass filter, band stop filter (detailed comments procedures for novice learning FIR digital filter))