Talk:Dual-tone multi-frequency signaling

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Replaced audio clip[edit]

I replaced the audio clip in the article. The old clip ( involved some DTMF tones, but seemed to focus on something else. Jaho (talk) 22:03, 29 March 2010 (UTC)

History and Introduction[edit]

According to the current article, DTMF was first introduced to the public at the NY World's Fair in 1964. It was, however, in full "field test" usage in multiple small towns in the US by then. Most notably, it was first used in Findlay Ohio in 1960 and then in Greensburg, PA in 1961. Is this distinct from a public "introduction" LotSolarin 09:03, 9 December 2006 (UTC)

...and you can use them to play tunes. There are web sites that give popular tunes for the phone. What note does each key correspond to? -- Tarquin

I've just tried it against a piano. The lower frequencies are approx. F♯, G, A and B♭ above Middle C and the higher ones are D, E, F♯ and G♯ of the next octave. (talk) 15:12, 28 July 2008 (UTC)

International Standard[edit]

Is this actually a international standard? Is it accepted world wide?

Actually, i have no clue what ringback means. It's found in the DTMF Event Frequencies table.

busy signal     480Hz   620Hz
dial tone       350Hz   440Hz
ringback (US)   440Hz   480Hz

Also: the articles says The frequencies were initially designed with a ratio of 21/19, which is slightly less than a whole tone.

Well, in my eyes, 21/19 is slightly more than a whole tone..

Thanks, --Abdull 13:42, 4 Apr 2005 (UTC)

Ringback is the tone played back through the phone handset when you're ringing someone. It is different in other countries, which is why there's a '(US)' next to it. --Shawn K. Quinn 04:05, 2005 Apr 11 (UTC)
There is another set of DTMF tones which is a CCITT/ITU standard. I am not sure what it is used for, the only use I know of is encoding calling number information in audio recordings (and I'm not sure it's still used even for that). It's a 3x4 matrix of tones if I remember right (with an "A" and "B" filling out the matrix after the digits). --Shawn K. Quinn 03:28, 2005 Apr 10 (UTC)
Abdull says: "Well, in my eyes, 21/19 is slightly more than a whole tone."
It is less than a whole tone. A whole tone has a ratio of 2^(1/6) = 1.122462 = 2 semitones = 200 cents. The ratio 21/19 = 1.105263 = 1.73 semitones = 173 cents.
The formula to convert a ratio to semitones is semitones(ratio) = 1200 * log(ratio) / log(2). [MatthewJ]
Yes, the DTMF frequencies listed here are an international standard and now used in much of thr world, including the U.K. & Republic of Ireland, Australia, New Zealand, France and most of Western Europe etc.
The supervisory tones (busy, ringback etc.) can vary for historical reasons though. The article seems a little muddled in this respect, and I'm not really sure why supervisory tones need to be listed in an article about DTMF dialing at all. (talk) 21:35, 19 August 2012 (UTC)

"Number spelling"[edit]

I don't know what "number spelling" is properly called, but how about an explanation of the association of letters and phone digits, which is getting rarer these days but still sometimes used in advertising, like "1-800-RENTCAR"? I guess a new article would be appropriate for this subject, since this can of course also be done with pulse dialing?

Telephone number has an appropriate section
Jim.henderson 00:31, 13 December 2006 (UTC)
Oh no it doesn't. (talk) 17:36, 8 November 2013 (UTC)

Bank Machines[edit]

The article says: "With the widespread introduction of computers and bank machines, the phone keyboard has become 'oddball', causing mistakes."

I would remove 'bank machines' from that sentence, because they have the same layout as phone keypads.

Jim Habegger 17:07, 9 December 2005 (UTC)

Besides which, I hardly think that "oddball" can legitimately be used to describe a keypad layout which is the norm on hundreds of millions of telephones worldwide. (talk) 21:38, 19 August 2012 (UTC)

DTMF waveform and spectrum images[edit]

These images are so low quality as to be essentially useless. The waveform one doesn't actually show the waveforms, all you can see is 3 white blocks, and it's almost impossible to see the tones in the spectrum image. The images should be removed from the article or replaced with higher quality images that actually convey useful information. Jibjibjib 09:27, 17 January 2007 (UTC)

Why don't the DTMF tone samples adhere to the media player standards of Wikipedia? I can't listen to samples of OGG files stored on the site. Please put something less proprietary up, or use an embedded player. —Preceding unsigned comment added by (talk) 20:53, 4 November 2009 (UTC)

Image copyright problem with Image:Autovon keypad.jpg[edit]

The image Image:Autovon keypad.jpg is used in this article under a claim of fair use, but it does not have an adequate explanation for why it meets the requirements for such images when used here. In particular, for each page the image is used on, it must have an explanation linking to that page which explains why it needs to be used on that page. Please check

  • That there is a non-free use rationale on the image's description page for the use in this article.
  • That this article is linked to from the image description page.

This is an automated notice by FairuseBot. For assistance on the image use policy, see Wikipedia:Media copyright questions. --10:36, 12 May 2008 (UTC)

Q: Why is the first image on the article page an example of the least common version of DTMF keypad in existence? An805Guy (talk) 08:35, 21 April 2010 (UTC)

Is it possibly to add something about sampling, analog to digital conversion and reconstruction of DTMF signals? —Preceding unsigned comment added by (talk) 15:26, 27 December 2008 (UTC)
It is a rare unit, however it is one of the only production units to use all 16 tone combinations in the DTMF specification. Most just used the 12 most common and since this article is about the full DTMF specification and you can see a 12 button DTMF set most anywhere, it seemed appropriate. Also, the previous photo was crap. In retrospect, having it at the top is potentially confusing. Does anyone have a good shot of a 12 button? I'll see if I can dig one up. Lexlex (talk) 04:55, 3 October 2010 (UTC)
And the earliest DTMF units released for customer use had only 10 buttons. The 12-button pads with * & # added didn't become standard issue until later in the 1960's. (talk) 12:07, 20 June 2013 (UTC)

Incomplete, over-complex sentence[edit]

Article says: "Due to DTMF over analog telephone lines in the voice-frequency band between telephone handsets and other communications-terminating devices and the switching center, the previously semiautomated system that needed human intervention from a telephone operator, who then dialed a sequence of MF digits that were then routed and switched via automation." Can anyone write this more clearly? I can't understand it at all - otherwise I'd have a go. --Northernhenge (talk) 22:39, 27 June 2010 (UTC)

Something Missing in the Special Tones Section[edit]

Great article, but in special tones section should be the Off-Hook Tone or at least a cross-reference to an already-existing Wikipedia article on such:

I don't know how to insert references. Feel free to do so.

It is true that the off-hook uses four tones, not two. But still, if you make a special section for special tones it is such a bother that one special tone (off-hook) is missing when there is otherwise very complete coverage of everything else.

Missing the off-hook tone in the special tonse section aside, superb article. I knew all the "what"s from books I had, but the why's and motivations -- that was new & quite nice. — Preceding unsigned comment added by (talk) 18:39, 16 August 2012 (UTC)

Hearing Just ONE of the two DTMF frequencies[edit]

A single frequency can be produced from most landline telephones. To get the row's frequency, chord (simultaneously push) two buttons from that row. You will hear only a single sinewave -- the one for that row. Similarly, chording two column buttons produces only the sinewave assigned to that column.

If you do these chordings whilst on a system that has menus (such as a voice mail system), be sure the chordings are exact; that is, make sure you don't have a single button only depressed (for 70+ ms), otherwise you will have activated that menu choice that corresponds to the number of the button.

The chording trick is a way to test fidelities throughout the system, from source (your landline phone) to playback (let's say you did the chording to a voice mail system).

But at home, in your earpiece, you can just do the chording to hear what each frequency alone sounds like.

Remember, chording doesn't work from cell phones and probably doesn't work from computerized / digital workplace phones. — Preceding unsigned comment added by (talk) 18:52, 16 August 2012 (UTC)

Multifrequency signaling, LD introduction[edit]

I am removing an incoherent paste which was linking introduction to the public of the push-button telephone to LD's technical problems. Further, the source intended for backing the date of November 18, 1963 in the first push-button telephone article could not be verified. --Askedonty (talk) 08:24, 14 September 2013 (UTC)