Editing DTMF signaling (section)

==Keypad==
[[File:DTMF keypad layout.svg|thumb|DTMF keypad layout]][[File:MultiTone1.png|thumb|right|Combination of 1209 Hz and 697 Hz sine waves, representing DTMF "1"]]
The DTMF [[telephone keypad]] is laid out as a matrix of push buttons in which each row represents the low  frequency component and each column represents the high frequency component of the DTMF signal. The commonly used keypad has four rows and three columns, but a fourth column is present for some applications. Pressing a key sends a combination of the row and column frequencies. For example, the ''1'' key produces a superimposition of a 697 [[Hz]] low tone and a 1209&nbsp;Hz high tone. Initial pushbutton designs employed levers, enabling each button to activate one row and one column contact. The tones are decoded by the switching center to determine the keys pressed by the user.

{| class="wikitable"
|+ DTMF keypad frequencies (with sound clips)<ref name="lancaster" />
|-
!align=center|
!align=center| 1209&nbsp;Hz
!align=center| 1336&nbsp;Hz
!align=center| 1477&nbsp;Hz
!align=center| 1633&nbsp;Hz
|-
!align=center| 697&nbsp;Hz
|align=center| {{Audio|Dtmf1.ogg|1}}
|align=center| {{Audio|Dtmf2.ogg|2}}
|align=center| {{Audio|Dtmf3.ogg|3}}
|align=center| {{Audio|DtmfA.ogg|A}}
|-
!align=center| 770&nbsp;Hz
|align=center| {{Audio|Dtmf4.ogg|4}}
|align=center| {{Audio|Dtmf5.ogg|5}}
|align=center| {{Audio|Dtmf6.ogg|6}}
|align=center| {{Audio|DtmfB.ogg|B}}
|-
!align=center| 852&nbsp;Hz
|align=center| {{Audio|Dtmf7.ogg|7}}
|align=center| {{Audio|Dtmf8.ogg|8}}
|align=center| {{Audio|Dtmf9.ogg|9}}
|align=center| {{Audio|DtmfC.ogg|C}}
|-
!align=center| 941&nbsp;Hz
|align=center| {{Audio|DtmfStar.ogg|&ast;}}
|align=center| {{Audio|Dtmf0.ogg| 0}}
|align=center| {{Audio|DtmfPound.oga|&num;}}
|align=center| {{Audio|DtmfD.ogg|D}}
|}