单音多频信号的产生和识别，采用FFT变换。应用于电话拨号。是学习数字信号处理的大作业。-Tone multi-frequency signal generation and recognition, the use of FFT transform. Applies to telephone dial-up. Digital Signal Processing is the study of large operations.

电话语音，可进行拨号连接，类似网络电话系统。-Telephone voice, dial-up connection can be similar to Internet telephony systems.