What is DTMF (Dual-Tone Multi-Frequency Singling)?

Last Update: August 9th, 2021


DTMF (or dual-tone multi-frequency signaling) is the sound a pressed telephone keypad. This sound is heard by the telephone company, which then uses the information to route the call or use a telephone feature.

DTMF keypads were responsible for replacing the rotary dialers on telephones.


Each key on a telephone keypad emits a pair of tones – one lower and the other higher. The phone company’s automatic switchboard can easily understand the two tones.

When dialing a phone number (or fax number), the pressed buttonsĀ tell the switchboard where the call should go.

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