DTMF – Dual-Tone Multi-Frequency

(DTMF) Dual-Tone Multi-Frequency- is a set of 16 tones used for in-band signaling between phone switches and telephones. Each key that is pressed generates two tones at specific frequencies, so that a voice or regular sound transmissions cannot mistakenly imitate the tones. One tone is generated from a high-frequency group and the second tone from a low frequency group.

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