I was thinking to add midi control to my calculator, with a small midi to controller converter that is actually used for gaming controls and is sold by Devision6 consolemidi. When you put down the horn you also have a tone. My calculator does not do that, only i have a few of them so by using two i could play the high priority notes. On a normal telephone it would be possible to dial those extra priority setting by pressing two numbers at once. That a really advanced telephone even has more dials they are combinations of numbers. In that way you can have a secured telephone line. It has extra notes for setting priority on a telephone line. On old telephones you are able to hold the speaker in front of the microphone and dial a telephone number. Then when you press dial it plays the dtmf tones. I have a old calculator that is able to store names with telephone numbers. Electric Circuits by Nilsson and Riedel, 10th edition, page 548. Update: Dial tone and busy signal Related posts The phone company wants tones that are easy to pull apart analytically.įinally, here are the chords that correspond to each button on the phone keypad. These tones are deliberately not in traditional harmony because harmonic notes (in the musical sense) are harmonically related (in the Fourier analysis sense). As with the column frequencies, the row frequencies are two octaves higher than written. The backward flat symbol in front of the A is a half flat. In musical terms, these notes are F, G (31 cents flat), A (54 cents flat), and B flat (16 cents sharp). Similarly, the four row frequencies, starting from the top, are 697, 770, 852, and 941 Hz. Notice that the symbol in front of the D is a half sharp, one half of the symbol in front of the F. In approximate musical notation, these pitches are two octaves above the ones written below. The third frequency, 1477 Hz, lands on an F#. The second frequency, 1336 Hz, is 23 cents higher than an E. The first frequency, 1209 Hz, is exactly between a D and a D#, two octaves above middle C. These do not correspond exactly to standard musical pitches. The three column frequencies are 1209, 1336, and 1477 Hz. I’ve long wondered what these tones would be in musical terms and I finally went to the effort to figure it out when I ran across DTMF in. This system is known as DTMF (dual tone multiple frequency). The sounds produced by a telephone keypad are a combination of two tones: one for the column and one for the row.

Telephone keypad