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f(Hz) | 1209 | 1336 | 1477 | 1633 |
697 | 1 | 2 | 3 | A |
770 | 4 | 5 | 6 | B |
852 | 7 | 8 | 9 | C |
941 | * | 0 | # | D |
The lower frequency (corresponding to the row) is emitted with less amplitude than the higher one, and precisely of 2 dB (that means that the amplitude is 1.259 times smaller). Every dtmf-dialtone has a length of 100ms followed by pause of 50ms length. The samplerate is 11025Hz (can't generate 8KHz on my PC ;-) with 8Bits mono.