
Dual Tone Multi Frequency is the signal to the phone company generated when you press a telephone's touch keys. It's known as a 'Touchtone' phone. DTMF has generally replaced loop disconnect ('pulse') dialling. With DTMF, each key you press on your phone generates two tones of specific frequencies.
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http://www.encyclo.co.uk/local/20632

Data Tone Multiple Frequency + Dual Tone Multifrequency
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Dual Tone Multi Frequency. Tone signaling used by fixed phones to replace pulse dialling and by mobile phones and fixed phones to control VAS (value added services), such as information service access. DTMF is often called `Touch-Tone`.
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Dual Tone Multifrequency. Signalling which is the basis of the operation of push-button telephone sets. Dialled numbers are transmitted as tones rather than electronic pulses.
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(Dual Tone Multi Frequency) is the dialling signal that you generate when you press an ordinary telephone's keys. It is known as 'Touchtone' phone (formerly a registered trademark of AT&T). With DTMF, each key you press on your phone generates two tones of specific frequencies. So that a voice can't imitate the tones, one tone is generated from a h...
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http://www.zoo.co.uk/~z0001325/Glossary.html

Dual tone multifrequency. Use of two simultaneous voice-band tones for dialing (such as touch tone).
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https://www.encyclo.co.uk/local/22803
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