DTMF meaning: What are DTMF tones?


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. Each of the individual number or symbol keys on the keypad has an assigned high- and low-frequency signal. 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.


How do DTMF tones work?


As mentioned above, DTMF tones are created by the synchronized combination of the high- and low-frequency signal. 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. The combination allows each key to produce a different and distinctive tone.


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. This process determines the exact number that an individual is dialing.


The keypad


DTMF allows for eight different frequencies on a keypad. 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. The low-frequency tones are 697 Hertz (Hz), 770 Hz, 852 Hz and 941 Hz, and each frequency is assigned a specific row. The high-frequency tones are 1209 Hz, 1336 Hz, 1477 Hz and 1633 Hz, and each frequency is assigned a specific column.


The keys typically include numbers 1-9, an asterisk (or star) key, a number 0 key and a pound key. Some telephone keypads include letter keys (A, B, C and D), which is placed in the additional column with the highest frequency.


These eight tones allow for 16 total keys on a keypad, as there are four unique high-frequency columns and four low-frequency columns. However, most standard phone keypads operate on a 12-key keypad­, omitting the high-frequency column that hosts four letters. These 12-key keypads have three high-frequency columns, and four low-frequency columns.


DTMF meaning: What is DTMF?


DTMF, dual-tone multi-frequency, is the signaling system used present day for a variety of phone technologies, such as cell phones, hand-set phones and voice over internet protocol (VoIP). The system is dual-tone and multi-frequency because each key pressed on the phone’s keypad utilizes two frequencies (a high- and low- frequency), or two tones, to submit a singular sound, or signal, associated with the key pressed.


While DTMF sends signals regarding the phone number that an individual wishes to connect to, it is also used to send a signal in an interactive voice response, which is an auto attendant menu.


Callers are sometimes met with an automated greeting after dialing a phone number they wished to reach. A variety of businesses use this automated greeting, often providing a menu prompt with options for the outcome of the call. The interactive voice response allows a caller to speak their selection or to press a key. By pressing a key to select a command, the caller is utilizing DTMF.


When the caller selects one of the menu options offered, the unique DTMF tone associated with the key selected is decoded into a command, directing the caller to their desired selection, such as reaching a specific employee or speaking with a representative.


DTMF today


DTMF is the signaling system most commonly used in present day. Prior to the technology’s invention, humans used pulse dialing to signal numbers, which are associated with rotary dialing in rotary phones. Pulse dialing was abandoned for a variety of reasons—it was slow and tedious, could not be used for long distance calls and was complicated to build and maintain.


The creation of DTMF allowed for a variety of phone technologies to prosper, furthering communications for families, friends, public services and businesses.


For example, DTMF has a significant role in VoIP, a technology that allows users to conduct phone calls by internet connection opposed to a mobile network. Utilizing DTMF, TollFreeForwarding.com offers a variety of calling services that gives individuals and business owners to make and manage phone calls from around the world.


For more information regarding a variety of phone technology and software topics, visit the TollFreeForwarding.com blog. If implementing cloud-based, toll-free phone numbers is a tool that seems ideal for your business, a virtual phone number can be easily attainable with TollFreeForwarding.com today.