These eight tones allow for 16 total keys on a keypad, as there are four unique high-frequency columns and four low-frequency columns. Some telephone keypads include letter keys (A, B, C and D), which is placed in the additional column with the highest frequency. The keys typically include numbers 1-9, an asterisk (or star) key, a number 0 key and a pound key. The high-frequency tones are 1209 Hz, 1336 Hz, 1477 Hz and 1633 Hz, and each frequency is assigned a specific column. The low-frequency tones are 697 Hertz (Hz), 770 Hz, 852 Hz and 941 Hz, and each frequency is assigned a specific row. Each key in the same row has the same low-frequency tone, and each key in the same column has the same high-frequency sound. This process determines the exact number that an individual is dialing.ĭTMF allows for eight different frequencies on a keypad. When the key is pressed, these two frequency signals are transmitted over telephone wires where technology listens to the specific sounds, decodes the sounds and turns the sounds into commands.
The combination allows each key to produce a different and distinctive tone. The high-frequency signal of a key is determined by the column that the key is in, and the low-frequency signal is determined from the row that the key is in.
By the push of a button, these frequencies are combined, allowing each key on the keypad to emit a sound that is unique to that key, otherwise known as the DTMF tone.Īs mentioned above, DTMF tones are created by the synchronized combination of the high- and low-frequency signal. Each of the individual number or symbol keys on the keypad has an assigned high- and low-frequency signal. Dual-tone multi-frequency tones, or DTMF tones, refer to the sounds produced by a telephone when the numbers on the telephone’s keypad are pressed by the user.
0 kommentar(er)
