DTMF (Dual Tone Multi Frequency) is a dual-tone signaling system similar to tone dialing used in telephones. The term DTMF is also used to refer to tone dialing itself. A synonym for this term is "Touchtone" (not widely used, as Touchtone is a registered trademark of AT&T). In DTMF mode, when a telephone key is pressed, a sound (tone) is generated that is a combination of two frequencies — one high and one low. Hence the name “Dual” (double).
The DTMF signaling system includes eight tones, specifically chosen so that they can be transmitted through the telephone network without attenuation and with minimal mutual interference. Since these tones fall within the frequency range of the human voice, additional measures were introduced to prevent voice from being mistaken for dialing tones. One such measure is dividing the tones into two groups: high-frequency and low-frequency. The table below lists DTMF tones for various digits (and control keys) on a push-button telephone and their corresponding frequency pairs. One hertz (Hz) is a frequency equal to one cycle per second.
Using tone dialing, it is possible to easily control computer telephony applications by responding to system prompts through pressing keys on the telephone keypad.
Digit Low Frequency High Frequency 1 697 Hz 1209 Hz 2 697 1336 3 697 1447 4 770 1209 5 770 1336 6 770 1447 7 852 1209 8 852 1336 9 852 1477 0 941 1336 * 941 1209 # 941 1477
Related articles: DCS, CTCSS, Telephone codes of cities in the Russian Federation