IIR

代码说明：

  归一化后截止频率为0.2的数字低通滤波器，并且能有效滤掉工频干扰，使心电信号有效表达信息。(The normalized digital low-pass filter with a cutoff frequency of 0.2, and can effectively filter out power frequency interference, so that the ECG signal can effectively express information.)