说明：  介绍了数字滤波器的设计基础及用窗函数法设计FIR滤波器的方法，运用MATHLAB语言实现了低通滤波器的设计并用CCS 进行观察效果。
(The design basis of digital filter and the method of designing FIR filter by window function method are introduced. The design of low-pass filter is realized by MATHLAB language and observed by CCS.)