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DTMF

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DTMF (engl. Dual-tone multi-frequency, myös Touch Tone tai Tone Dialing) on puhelinlaitteissa käytetty numeroiden äänitaajuusvalinta. Aikaisemmin käytettiin hidasta impulssivalintaa, jossa valittava numero ilmoitetaan pulssien määrällä pulssisarjoissa. Äänitaajuusvalinnassa kukin numero on koodattu kahdeksi toisiinsa epäharmonisessa suhteessa olevan taajuuden muodostamaksi ääneksi. Näin varmistetaan, että käytännössä mitkään luonnolliset äänet eivät puhelimen mikrofoniin tullessaan pääse aiheuttamaan virheellistä numerovalintaa.[1]

Näppäintä vastaavat taajuudet
1 209 Hz 1 336 Hz 1 477 Hz 1 633 Hz
697 Hz 1 2 3 A
770 Hz 4 5 6 B
852 Hz 7 8 9 C
941 Hz * 0 # D

Lähteet

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  1. ↑ Technical Features Q.23. International Telecommunication Union ITU. Viitattu 9.7.2017.
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DTMF
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