IIR

代码说明：

  按照给定指标采用模拟低通滤波器（巴特沃思低通或者切比雪夫低通）去逼近理想模拟低通滤波器 ，然后通过双线性变换法对模拟滤波器进行数字化，得到数字滤波器 。(According to a given target analog low-pass filter (Butterworth or Chebyshev low-pass low-pass) to approximate the ideal analog low-pass filter, then through the bilinear transformation method to digitize the analog filters, digital filters has been .)