DTMF is the abbreviation of Dual Tone Multi-Frequency, that is, dual-tone multi-frequency. It refers to the sound or tone that the phone makes when pressing a number, where each key has two tones of a specific frequency, which are then transmitted over the voice channel.
DTMF can be combined in a total of 16 character forms, of which 10 numbers are 0 to 9, and 6 represent functions *, #, A, B, C, D. Dual-tone multi-frequency of DTMF, in which dual-tone refers to the audio signal composed of two frequencies, namely high-tone group and low-frequency group, and multi-frequency refers to multiple frequencies in two sound groups.
DTMF operation is simple, fast, high transmission speed, reliable transmission technology, and strong anti-interference ability, so it is widely used in walkie-talkie communication systems. Common functions are PTT ID transmission, selcall, call alert, ACK , etc.