产生一个连续信号，包含低频，中频，高频分量，对其进行采样，进行频谱分析，分别设计三种高通，低通，带通滤波器对信号进行滤波处理，观察滤波后信号的频谱。-generating a continue time singal,which contains low,middle and high frequences,sampling it.analisize its spetrum.Then designing three kind filters are lowpass,highpass,bandpa