I chanced upon a technical description of the Touch-Tone system. The book I was reading had an explanation of how each key on a telephone sends a combination of two tones down the wire ...

One late night many decades ago, I chanced upon a technical description of the Touch-Tone system. The book I was reading had an explanation of how each key on a telephone sends a combination of ...

Each digit has a physical button that transmits a different audio tone when depressed. Known as the dual-tone multifrequency (DTMF) system, the signal is a combination of the row and column ...