Talk:Dual-tone multi-frequency

From Wikipedia, the free encyclopedia

 Please help improve this article or section by expanding it.
Further information might be found on the talk page or at requests for expansion. (January 2007)

Contents

[edit] History and Introduction

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

[edit] International Standard

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]

[edit] "Number spelling"

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)

[edit] Bank Machines

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 192.131.239.250 17:07, 9 December 2005 (UTC)

[edit] DTMF waveform and spectrum images

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)

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

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)