DTMF Decoder
Read the number dialled from a recording of telephone keypad tones.
You can also drag a file here. WAV, MP3, OGG, FLAC and M4A all work, and nothing is uploaded — the decoding happens in your browser.
Dialled
Each keypress
| # | Key | Start | Length | Tones |
|---|
No keypresses found. If you can hear the tones, the recording may be quiet or heavily compressed. Try the Spectrogram Viewer to see whether the pairs of tones are really there.
What DTMF is
Every key on a telephone keypad sends two tones at once: one picked from a low group, according to the row, and one from a high group, according to the column. Pressing 5 sends 770 Hz and 1336 Hz together. Two tones rather than one makes the signal hard to imitate by accident, which is why speech on a line does not dial numbers by itself.
That same property makes the decoding reliable. A frame of audio only counts as a keypress when exactly one low tone and one high tone stand clearly above the rest, so music and speech are rejected rather than producing plausible-looking digits.
Caches use this to hide coordinates in a recording of a phone being
dialled. The * and # keys, and the rarely-seen
A to D, are all decoded too. Puzzle setters
like them precisely because they're unexpected.