对FIR数字滤波器频域实现错误观点的讨论

Discussing of a Wrong Viewpoint about the Realization of FIR Digital Filter in the Frequency Domain

关于FIR数字滤波器的频域实现存在一种错误的观点和做法,即直接在离散傅利叶变换域将输入信号属于阻带的谱线清零,而属于通带的谱线保留,再离散傅利叶反变换到时域,并且认为通过这种方法得到的信号是对输入信号理想滤波的结果。本文针对这一观点,利用频域取样的概念,从时域和频域两个角度分析,指出该做法并不能实现理想滤波,并且滤波性能通常不能达到指标要求。

There is a wrong viewpoint about the realization of FIR digital filter in the frequency domain. The way is to clear the DFT spectrum lines of the input signals in the stop band, and to remain the ones in the pass band. Then the DFT is changed to the time domained by IDFT. This viewpoint thinks that the obtained signal is the output of an ideal filtering to the input signal. This paper discusses the viewpoint from both the time domain and the frequency domain by using the concept of frequency domain sampling, and points out that this method can＇t realize ideal filtering.