DTMF
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Intro
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| 1209 Hz | 1336 Hz | 1477 Hz | 1633 Hz | |
|---|---|---|---|---|
| 697 Hz | 1 | 2 | 3 | A |
| 770 Hz | 4 | 5 | 6 | B |
| 852 Hz | 7 | 8 | 9 | C |
| 941 Hz | * | 0 | # | D |
https://en.wikipedia.org/wiki/Dual-tone_multi-frequency_signaling
Goertzel
[edit | edit source]https://en.wikipedia.org/wiki/Goertzel_algorithm