说明：  生成2KHz和8KHz的混合信号,使该信号通过上述滤波器,观察滤波前后的波形变化和频谱分布情况, 在改信号中加入高斯白噪声,
(The mixed signal of 2KHz and 8KHz is generated so that the signal passes the above filter, the waveform change and spectrum distribution before and after filtering are observed, and Gao Si white noise is added to the modified signal.)