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，分别设计低通，带通，高通滤波器对信号进行滤波处理，观察滤波前后信号的频谱。-Generates a continuous signal, including low-frequency, medium frequency, high frequency components, its sampling, spectral analysis, were designed low-pass, band pass, high pa