All About " DTMF ( Dual Tone Multi- Frequency Signaling) "

All About " DTMF ( Dual Tone Multi- Frequency Signaling) "

Dual-tone multi-frequency signaling (DTMF) is an in-band telecommunication signaling system using the voice-frequency band over telephone lines between telephone equipment and other communications devices and switching centers. DTMF was first developed in the Bell System in the United States, and became known under the

trademark Touch-Tone for use in push-button telephones supplied to telephone customers, starting in 1963. DTMF is standardized by ITU-T Recommendation . It is also known in the UK as MF4.

The Touch-Tone system using a telephone keypad gradually replaced the use of rotary dial and has become the industry standard for landline and mobile service. Other multi-frequency systems are used for internal signaling within the telephone network.

DTMF keypad frequencies (with sound clips)       

              

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

DTMF was originally decoded by tuned filter banks. By the end of the 20th century, digital signal processing became the predominant technology for decoding. DTMF decoding algorithms often use the Goertzel algorithm to detect tones.

Source :- wikipedia