DTMF tone generator and decoder in your browser
Every key on a phone sends two tones at once: one from a low group and one from a high group. This system is called DTMF (dual-tone multi-frequency), or touch tone. This DTMF tone generator plays all 16 keys, dials a whole sequence and saves it as a WAV file. The built-in DTMF decoder reads the digits back from a recording or live from your microphone.
Use it to test an IVR menu, an intercom or a radio link, to make tones for a video, or to find out which number was dialled on a recording you made. Everything runs in your browser; audio you decode is not uploaded.
How to use the DTMF Tone Generator & Decoder
- Press and hold a key on the keypad, or type 0–9, *, # or A–D, to hear its tone pair.
- Under Dial a sequence, type the digits and set the tone and gap length, the level and the twist.
- Press Play sequence to hear it, or Download WAV to save it. Add background noise if you want to test a receiver.
- To decode, drop an audio file on the box or press Listen with microphone and play the tones near it.
- Read the digits and the table of timings and levels; Copy digits copies them.
DTMF Tone Generator & Decoder features
All 16 keys
Digits, * and #, plus the A–D column used by radio and military phones.
Exact WAV output
16-bit mono at 8, 16, 44.1 or 48 kHz, with 5 ms soft edges so the tones do not click.
Adjustable signal
Tone and gap length, level per tone, twist and optional white noise at a set signal-to-noise ratio.
Goertzel decoder
Finds each digit with its start time, length, levels and twist.
Live microphone mode
Decodes as you listen, through an AudioWorklet that sees every sample.
DTMF frequencies (ITU-T Q.23)
The table is Figure 1 of ITU-T Recommendation Q.23 (1988), which also says each frequency must be within ±1.8% of nominal and that distortion products must be at least 20 dB below the tones. No frequency is a simple multiple of another, so speech and music rarely imitate a key.
| 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 |
How the decoder works
The audio is converted to 8 kHz mono and cut into blocks of 205 samples (25.6 ms) that overlap by half. The Goertzel algorithm measures the strength of each of the eight frequencies in a block — like a fast Fourier transform that only computes eight bins. A block counts as a key when one low and one high tone are both clearly present (each at least 6 dB above the other tones of its group), the high tone is between 8 dB weaker and 4 dB stronger than the low one, and the two tones carry at least half of the block’s energy. A digit is reported after two such blocks in a row (about 40 ms) and released after two blocks without it.
Those limits follow the receiver values one administration lists in ITU-T Q.24 Annex A (twist +4 to −8 dB, signals of at least 40 ms). The decoder does not enforce Q.24’s exact frequency limits (operate within 1.5%, reject beyond 3.5%): it accepts what falls inside a Goertzel bin, about ±2–3%.
Tips for clean decoding
- Record at least 40 ms of tone and 40 ms of silence per digit; fast auto-dialers can be shorter than that.
- Turn off noise suppression in call-recording apps: it can remove tones it treats as noise.
- Heavily compressed audio (low-bitrate phone calls, voice notes) may smear tones; try the original recording.
- To see the tones, open the file in the audio spectrogram. For a single test frequency, use the tone generator.
DTMF Tone Generator & Decoder FAQ
What are DTMF tones?
They are the sounds a phone keypad makes. Each key sends one low frequency (697–941 Hz) and one high frequency (1209–1633 Hz) together, so the exchange or the answering system can tell which key was pressed.
Can this DTMF tone generator dial a phone number?
It can play the tones of any number through your speaker, and many phones and systems will accept them that way. It does not connect a call by itself.
How do I decode DTMF from a recording?
Drop the audio file on the decoder box. The digits appear with their timings. WAV and MP3 work in every browser; M4A and OGG depend on the browser.
Why does the decoder miss some digits?
Tones that are very short, very quiet, clipped or buried under speech fail the checks. Try a cleaner copy, or raise the volume and play it to the microphone.
What are the A, B, C and D keys?
They are the fourth column of the standard keypad. Ordinary phones leave them out; they are used in some radio, alarm and network-control systems.
Is my audio uploaded?
No. Files and microphone audio are analysed in your browser and are not sent anywhere.