Have you ever tried to guess someone’s phone number just by listening to the telephone keypad tones that the push buttons made? No matter how hard your little ears strained to hear those pitches, you would never get the numbers right. You were actually trying to decode DTMF. Dual Tone Multi-Frequency (DTMF) signaling, the technology that makes such pretty music on your smartphone, cannot be discerned by the human ear! Each DTMF tone is actually a combination of sounds from two frequencies – one low, and one high – so it can’t be reproduced by the human voice, either (unless you’re a Tuvan throat singer–what??).
DTMF was introduced by AT&T in 1963, and subsequently became trademarked as Western Electric’s Touch Tone. In the 1970s, rotary models were eventually phased out by the touch-tone phone. So for anyone born let’s say after 1980, you’re probably too young to remember rotary dial.
Nowadays, DTMF technology is used in call centers and paired with interactive voice response (IVR) software to navigate in-call menus and gather sensitive data like credit card numbers and birthdates. It reduces the likelihood of errors, acts as an information security measure, and can even speed up call processing times. A whirlwind tour of this invention can be found in the infographic below! For more in-depth information, please explore our paper to learn what is DTMF technology.