说明：  频分复用(FDM，Frequency Division Multiplexing)的matlab实现，仿真时录入三路声音信号进行处理，将用于传输信道的总带宽划分成三个子频带，经过复用以后再将录入的声音信号恢复出来。
(FDM (frequency division multiplexing) is realized by MATLAB. In the simulation, three sound signals are input for processing. The total bandwidth used for transmission channel is divided into three sub bands. After multiplexing, the input sound signals are recovered.)