Path: utzoo!attcan!uunet!cs.utexas.edu!sun-barr!texsun!texbell!vector!telecom-gateway From: wales@cs.ucla.edu (Rich Wales) Newsgroups: comp.dcom.telecom Subject: DTMF Frequencies From a Musician's Point of View Message-ID:Date: 9 Aug 89 19:54:04 GMT Sender: news@vector.Dallas.TX.US Reply-To: Rich Wales Organization: UCLA CS Department, Los Angeles Lines: 61 Approved: telecom-request@vector.dallas.tx.us X-Submissions-To: telecom@eecs.nwu.edu X-Administrivia-To: telecom-request@vector.dallas.tx.us X-TELECOM-Digest: volume 9, issue 284, message 1 of 9 In article Mike Morris gives the DTMF tones as follows: 1209 1336 1477 1633 697 1 2 3 A FO 770 4 5 6 B F 852 7 8 9 C I 941 * 0 # A D P Note that these frequencies occur in a well-tempered scale with a mul- tiplier between steps of 1.05135 (i.e., 13.84 steps per octave). If "tone N" has a frequency of 697*(1.05135^N), we get the following: 697.0 Hz = tone 0 1209.1 Hz = tone 11 770.4 Hz = tone 2 1336.4 Hz = tone 13 851.6 Hz = tone 4 1477.2 Hz = tone 15 941.3 Hz = tone 6 1632.8 Hz = tone 17 This particular well-tempered scale fits each of the stated frequencies to within 0.5 Hz, if you assume that 697 Hz is exact by definition. I suppose it might be possible to come up with an even better fit via a least-squares linear approximation to the logarithms of the frequencies. The upper set of tones is selected in such a way as to be roughly half- way between the octaves of the lower set of tones. That way, there is no chance for the upper tone of any pair to be "lost" in the harmonics from the lower tone. I'm not sure why they didn't use a scale with exactly 14 steps per octave (multiplier = 1.05076). That would seemingly have been simpler. The reason why you can do crude approximations to a few common tunes (e.g., "Mary Had a Little Lamb") with DTMF tones is that the Western musical scale is built on 12 steps per octave (multiplier = 1.05946) -- fairly close to the DTMF scheme if you don't stretch it too far. I have an old 5-line 4-wire Autovon phone here that I modified (added a network) for 25-pair 2-wire use. It has a "A" on the key that would normally be a "#". The 4th column keys are labeled with FO-F-I-P. I recall someone mentioning on TELECOM, some time ago, that Autovon used the keys in the 4th column to indicate the precedence of the call. The abbreviations mean something like "Priority", "Immediate", "Flash", and "Flash Override" (the latter heralding World War III for all practical purposes). By pressing one of these keys before dialing a number -- and assuming that your phone line had authorization to invoke that particu- lar precedence -- the Autovon system would automatically disconnect any call in progress of *lower* precedence in favor of your call. (I'm not sure whether the disconnected party got any kind of notification of why he had suddenly gotten cut off.) Maybe someone who has used Autovon can confirm this info and/or correct my details. -- Rich Wales // UCLA Computer Science Department // +1 (213) 825-5683 3531 Boelter Hall // Los Angeles, California 90024-1596 // USA wales@CS.UCLA.EDU ...!(uunet,ucbvax,rutgers)!cs.ucla.edu!wales "K-9, I think we're going to find out what it's like to be a cricket ball."