双音多频，由高频群和低频群组成，高低频群各包含4个频率。一个高频信号和一个低频信号叠加组成一个组合信号，代表一个数字。DTMF信号有16个编码。利用DTMF信令可选择呼叫相应的对讲机。-Dual tone multi-frequency, high-frequency and low-frequency group composed of groups, high-frequency group contains four frequencies each. A high-frequency signal and a low frequency signal is superimposed to form a combined signal representative of a number. DTMF signal has a 16 code. DTMF signaling to　the appropriate use of the intercom call.