说明：  是小学期课程设计的题目，ML法能够很好的估计信号的信噪比,FIR 底通和带通滤波器和IIR 底通和带通滤波器。
( Is the topic of the elementary school stage curriculum design, ML estimation method can be a good signal to noise ratio, Bottom-pass and band-pass FIR and IIR filter bottom pass and band-pass filter.)