The book I was reading had an explanation of how each key on a telephone sends a combination of two tones down the wire, and what’s more, it listed the seven audio frequencies needed for the ...

Known as the dual-tone multifrequency (DTMF) system, the signal is a combination of the row and column frequencies of the digit key. THIS DEFINITION IS FOR PERSONAL USE ONLY. All other ...

These analog phone systems use Dual Tone Multi Frequency (DTMF) signals in order to audibly represent all of the keys on a telephone keypad and place calls. [Brad] over at LucidScience decided ...