The sounds used for touch tone dialing are refered to as DTMF
(Dual Tone Multiple Frequencies) tones. Each number (as well
as the "#" and "*") is represented by a pair of tones. For
instance, the number "1" is represented by the frequencies 1209 Hz
and 697 Hz.
The following table shows the DTFM frequencies and the
corresponding keys.
Key | Frequency #1 | Frequency #2 |
1 | 697 Hz | 1209 Hz |
2 | 697 Hz | 1336 Hz |
3 | 697 Hz | 1477 Hz |
A | 697 Hz | 1633 Hz |
4 | 770 Hz | 1209 Hz |
5 | 770 Hz | 1336 Hz |
6 | 770 Hz | 1477 Hz |
B | 770 Hz | 1633 Hz |
7 | 852 Hz | 1209 Hz |
8 | 852 Hz | 1336 Hz |
9 | 852 Hz | 1477 Hz |
C | 852 Hz | 1633 Hz |
* | 941 Hz | 1209 Hz |
0 | 941 Hz | 1336 Hz |
# | 941 Hz | 1477 Hz |
D | 941 Hz | 1633 Hz |
DTMF "Touch" Tones are defined in CCITT Volume VI: General
Recommendations on Telephone Switching and Signalling
Recommendation Q.23: Technical Features of Push-Button Telephone
Sets."
|