DTMF (Dual tone multiple frequency) as the name suggests uses a combination of two sine wave tones to represent a key. These tones are called row and column frequencies as they correspond to the layout of a telephone keypad. DTMF is a signaling system for identifying the keys or better say the number dialed on a pushbutton or DTMF keypad. The early telephone systems used pulse dialing or loop disconnect signaling. This was replaced by multi frequency (MF) dialing. DTMF is a multi frequency tone dialing system used by the push button keypads in telephone and mobile sets to convey the number or key dialed by the caller. DTMF has enabled the long distance signaling of dialed numbers in voice frequency range over telephone lines.
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