A DTMF generator refers to any electronic device capable of generating dual tone multi-frequency (DTMF) signals used for dialing touch-tone telephones. The DTMF dialing system operates by configuring a keypad in a three column by four row grid representing the numbers 0 through 9 and other special characters such as the # and * keys. The touch pad grid is arrayed by assigning a specific high frequency for each column and a designated low frequency for each row.
When a user presses a digit on the keypad, a dual tone is generated that represents the intersection of the two distinct frequencies assigned for each column and row on the grid. For example, when the "2" digit is pressed on the keypad, a unique audio sinusoidal tone is emitted by mixing a pure high frequency of 1,336 Hz with a pure low frequency of 697 Hz. The DTMF signal tone generated by the keypad is then transmitted to the local office of the phone company where it is translated or decoded into the appropriate corresponding digits which allow the designated phone number to be dialed.
The first commercial application of a DTMF generator was the introduction of the touch-tone pad dialing system, first offered by AT&T to its customers in 1963. The touch-tone dialing system was demonstrably faster and more convenient than the mechanically based rotary dial pulse system, which it supplanted. After its introduction, touch-tone became the standard dialing system for telephones in the United States and was eventually adopted worldwide.
Touch-tone dialing permits activation and communication with DTMF-compliant equipment. This type of dialing allows users to control answering machines remotely and to activate and interface with many call routing, voice mail systems, or other auxiliary telephonic devices that can decode signals produced by a DTMF generator. Telephones equipped with DTMF-based touch-tone dialing allow consumers to access their account balances at banks, as well as retrieve other information from organizations that provide a telephonic interface based on the DTMF system.
A computer equipped with a sound card and digital audio software is capable of acting as a DTMF generator by producing the dual tone multi-frequencies used on touch-tone telephone keypads. The software program interprets the phone digits and then generates the appropriate audio files that conform to the standardized DTMF paired frequency tones. The dialing process can be activated either by a mouse click or through keyboard commands. This allows for rapid automated computer dialing of outgoing telephone numbers and is used by many businesses.