When a telephonic key is pressed, sounds are produced called Dual Tone Multi Frequency, or DTMF for short. Otherwise known as the “touch tone,” a different frequency is assigned to each key in the telephone – one low frequency and another high frequency – that sound simultaneously when a key is pressed. This two-tone combination makes it nearly impossible to reproduce with the human voice.
Once primarily used for telephone signaling to and from the local exchange, it now has a variety of applications in telecommunications and call center industries. DTMF technology supports acoustic transfer, which means that DTMF tones can be transmitted by a speaker and received by a microphone. Today, this technology is the dialing and switching communication standard.