Dual Tone Multiple Frequency (DTMF)

Dual Tone Multiple Frequency

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What is DTMF (Dual Tone Multiple Frequency)?

The audio signaling method used by Touch-Tone phones. Microsoft’s Telephony Application Programming Interface (TAPI) can recognize and interpret Dual Tone Multiple Frequency (DTMF) signals, allowing Microsoft Windows–based applications to integrate with telephony.

Some networking vendors also supply hardware devices called DTMF/ASCII converters, which convert DTMF tones directly into different ASCII characters, which can then be fed as input into a program that routes telephone calls accordingly.

How it works

Each DTMF signal generated by pressing a key on a Touch-Tone phone generates two simultaneous audible tones of different frequencies, as shown in the following table. DTMF was developed by AT&T; the term Touch-Tone was originally an AT&T trademark.

Frequencies of DTMF Signals

  697 Hz 770 Hz 852 Hz 941 Hz
1209 Hz
1
4
7
*
1336 Hz
2
5
8
0
1477 Hz
3
6
9
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