Dual-tone multi-frequency facts for kids
DTMF stands for Dual-tone multi-frequency. It's the special sounds your telephone makes when you press a button. Each number button on your phone makes a unique sound. Telephone systems listen to these sounds. They then know exactly which number you pressed.
When you press all the numbers for a phone number, it's called dialing the telephone. The phone system uses these sounds to connect your call. If someone calls you, your phone makes a loud sound. This is called ringing.
Telephones also have a star (*) button and a pound (#) button. These buttons also make different DTMF sounds. They are not part of the phone number itself. Instead, they can be used for other things. For example, you might use them to choose options in an automated menu.
Some special telephones even have letter buttons like A, B, C, and D. These buttons also create their own unique DTMF sounds.
How DTMF Works
When you press a button on your phone, it doesn't just send a single sound. It sends two different musical tones at the same time. These two tones are combined to create one unique sound for each button. That's why it's called "dual-tone."
For example, when you press the "1" button, your phone sends a low tone and a high tone together. The phone company's equipment hears this special combination. It then knows you pressed "1." Every button has its own special pair of tones. This system helps phone networks understand what you are dialing very quickly and accurately.
History of DTMF Tones
Before DTMF, people used to dial phones differently. Older phones had a spinning dial. When you turned the dial, it sent electrical pulses. This was called pulse dialing. It was slower than DTMF.
DTMF was invented by engineers at Bell Labs in the United States. It was first introduced in 1963. The new system was much faster. It also made it easier to use phones for things like automated banking or voicemail menus. This technology changed how we interact with phones. It made them more useful than just for talking.
Where DTMF is Used Today
You might think DTMF is only for old landline phones. But it's still used a lot today!
- Phone Menus: When you call a company and it says, "Press 1 for sales, press 2 for support," you are using DTMF.
- Voicemail: You use DTMF tones to navigate your voicemail messages.
- Remote Control: Some systems use DTMF to control things from far away. For example, you might use your phone to turn on a security system.
- Modems: In the past, DTMF was used by modems to connect computers over phone lines.
Even with new technologies like smartphones, the basic idea of DTMF tones is still important for many phone services.
Images for kids
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The keypads on telephones for the Autovon systems used all 16 DTMF signals. The red keys in the fourth column produce the A, B, C, and D DTMF events. In this case the letters indicate the precedence (urgency) of the call; (from lowest (at the bottom) to highest; Priority, Immediate, Flash or Flash Override
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Combination of 1209 Hz and 697 Hz sine waves, representing DTMF "1"
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Two CMD CM8870CSI DTMF Receivers
See also
In Spanish: Marcación por tonos para niños
