首先生成低频、中频、高频三种频率信号，再合成为连续信号，对连续信号抽样、频谱分析、并设计低通、带通、高通三种滤波器进行滤波-First generation low, intermediate and high frequency three frequency signal and re synthesis for continuous signal, the continuous signal sampling, spectrum analysis, and design low-pass, bandpass, highpass filter to filter