说明：  .用产生三种不同波形，分别计算并显示它们的单边频谱及功率谱，显示低通、带通、带阻、高通四种不同的滤波效果，体会滤波器的使用。
(Three different waveforms are produced, and their single side spectrum and power spectrum are calculated and displayed respectively, which show four different filtering effects, such as low pass, bandpass, band resistance and high pass, and realize the use of the filter.)