说明：  设计低通，带通，带阻数字滤波器，画出该滤波器幅频图、相频图，将原信号作为该滤波器的输入，计算响应；画出响应时域波形和谱图。
(Design low-pass, band-pass and band stop digital filters, draw the amplitude frequency diagram and phase frequency diagram of the filter, take the original signal as the input of the filter, calculate the response, and draw the response time-domain waveform and spectrum.)