Definition: Touch-Tone

The dialing technology in an analog telephone. 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 frequencies of the digit key.

The first touch-tone phones were installed in two Pennsylvania towns in the early 1960s. Digital phones do not use the Touch-Tone system. Contrast with rotary dial. See analog phone and digital phone.

Four Rows - Three Columns

Each row and each column in the keypad matrix is assigned a different frequency, and the audio signal transmitted is a superimposition of the two frequencies of the depressed key.