Dual Tone Multifrequency

 

Dual Tone Multifrequency (DTMF)

 

DTMF is the tones heard when pressing a button on a telephone. Those tones are comprised of two tones played together (thus the name "dual tone"), as shown in the table below. These are defined in ITU-T Recommendation Q.23.

	1209Hz	1336Hz	1477Hz	1633Hz
697Hz	1	2	3	A
770Hz	4	5	6	B
852Hz	7	8	9	C
941Hz	*	0	#	D

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