What is DTMF? | How Does it Work? |

Have you ever wondered how your telecom operator comes to know which number you have dialed? Whether you made a phone call or press buttons while talking to customer care number. Well, going into the history of the telephones, we previously used rotatory type dials which are now obsolete. This early telephones used pulse dialing or loop disconnect signaling and this signaling system need a telecom operator between the caller and the callee to detect the number dialed. This system requires almost 12 to 13 sec to detect a telephone number, which was very long compared to the present situation.

What is DTMF?

DTMF or (Dual-tone multi-frequency) is signaling System used to detect the number dialed on the push-down or DTMF keypad. This technology helps the telephone switching centers to automatically detect the dialed number and therefore, they no more need an operator as needed in pulse loop dialing. Also, DTMF technology only requires 1 sec to detect a number.

How DTMF Works?

As the name says, Dual tone, every key has a pair of frequency in Hz associated with it and it produces a voice like signals which enables the receiver to detect the key dialed. Both the sender and receiver have a DTMF chip in their phone. The frequency for all the keys is the mixture of row and column frequency. The Row frequency is also called as low group frequency and Column frequency are called as high group frequency. The frequencies are chosen such that the harmonics of both high group and low group frequency doesn’t come up with another standard frequency.

High group Frequency

All keys in a column have same frequency like

1, 4, 7, * has 1209 Hz Frequency

2, 5, 8, 0 has 1336 Hz,

3, 6, 9, # has 1477 Hz and
A, B, C, D has 1633 Hz.

Low group Frequency

All keys in a row have same frequency like

1, 2, 3, A has 697 Hz frequency

4, 5, 6, B has 770 Hz,

7, 8, 9, C has 852 Hz and

*,  0,  #, D has 941 Hz.

Therefore, DTMF technology is used in auto detecting of the dialed numbers. I hope this information helps. Finally, Thank you.