【磨刀不误砍柴工】由传递函数绘出频率响应图
用三阶低通IIR的传递函数来绘制频率响应图：H(z)=0.05634(1+z−1)(1−1.0166z−1+z−2)(1−0.683z−1)(1−1.4461z−1+0.7957z−2).H(z)=\frac{0.05634(1+z^{-1})(1-1.0166z^{-1}+z^{-2})} {(1-0.683z^{-1})(1-1.4461z^{-1}+0.7957z^{-2})}.H(z)=(1−0.683z−1)(1−1.4461z−1+0.7957z−2)0.056
