Dual Tone Multi Frequency - A nerdy term for describing push button or
Touch Tone dialing. (
Touch Tone is a registered trademark of
AT&T.)
In
DTMF, when you touch a button on a push-button dial, it makes an audible tone. The tone produced is actually a combination of two tones, one high frequency and one low frequency. Hence the name "
Dual Tone
Multi Frequency". In U.S. telephony, there are actually two types of
DTMF signaling - one that is used on normal business or home push-button/Touch Tone phones, and one that is used for signaling the
telephone network itself (T103 within T101). When you go into a
central office, look for the test-board. There you will see what looks like a standard Touch Tone pad. Next to the pad there will be a small toggle switch that allows you to choose the sounds the Touch Tone pad will make - - either normal Touch Tone dialing or the
network version.
| DTMF Tones |
High Group (Hz) |
| . |
1209 |
1336 |
1477 |
1633 |
|
| . |
697 |
1 |
2 |
3 |
A |
| Low |
770 |
4 |
5 |
6 |
B |
| Group |
852 |
7 |
8 |
9 |
C |
| (Hz) |
941 |
* |
0 |
# |
D |
