DTMF(Dual Tone Multi Frequency)信号是音频电话的拨号信号。由美国AT&T贝尔实验室研制, 双音多频信号编码技术易于识别，抗干扰能力强，发号速度快，且比用modem进行远程传输的方法更为经济实用,因此这种拨号方法取代了传统的脉冲拨号。

电话中的双音多频信号有两种用途：一是用于双音多频信号的拨号，去控制交换机接通被叫的用户电话机；二是利用双音多频信号遥控电话机各种动作，如播放留言，语音信箱。这些都离不开DTMF信号的产生。

有详细的需求分析 功能说明 流程图及代码。

-DTMF (Dual Tone Multi Frequency) signal tone phone dialing signal. Developed by AT &　T Bell Laboratories, dual-tone multi-frequency signal coding techniques are easy to identify, anti-interference ability and the number issued faster, more economical and practical than the modem for remote transmission, this dialing method to replace the traditional pulse dialing. Telephone dual tone multi-frequency signal has two purposes: one for dual tone multi-frequency signal a dial to control the switch is turned on the called subscriber telephone　second is the use of dual tone multi-frequency signal remote telephone various action, such as playing a message, voice mail. These are inseparable from the generation of DTMF signals. Detailed needs analysis of flow chart and code.