Phone Tones: The hidden language of phone number beeps
Twenty Thousand Hertz
00:00
DTMF Tones - What Are They?
DTMF tones were used by TV networks to insert local commercials into national broadcasts. In the 60s, a group of college students figured out how to manipulate the receiving machines with these tones. Even after phones started using DTMF to communicate with switching equipment, calls were still connected using those original MF tones.
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