Dtmf tone11/20/2023 ![]() 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. ![]()
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