DTMF Generator

Play touch-tone keypad sounds and dial a sequence.

Everything runs in your browser. No audio is ever uploaded.

Keypad

	1209 Hz	1336 Hz	1477 Hz	1633 Hz
697 Hz
770 Hz
852 Hz
941 Hz

Hold a key with the mouse or a finger to play it. With the keyboard, move focus to a key and hold Space or Enter.

Sequence

Each key plays for 70 ms with a 70 ms gap, the timing the phone network expects. Characters that are not keys are skipped.

Audio starts on your first tap on Play, as required by your browser.

A DTMF generator plays the touch tones a telephone keypad sends. Every key on this dial pad is a pair of sine tones, one from its row and one from its column, and this touch tone generator plays them one at a time while you hold a key, or in sequence when you type a number and dial it.

How to use it

Hold a key to play it. Mouse and touch both work, and from the keyboard you move focus to a key and hold Space or Enter. The tone lasts exactly as long as you hold, which is what you want when a menu is slow to react.
Read the pair off the pad. The row frequency runs down the left edge and the column frequency across the top, so the 5 key is 770 Hz and 1336 Hz, and every key names both frequencies to a screen reader.
Type a number in the sequence field and press Dial the sequence. Each key sounds for 70 ms with a 70 ms gap, the timing the phone network expects, and anything that is not a key, such as a dash or a space, is skipped.
Get the audio into the system that has to hear it. A cable or a virtual audio device is far more reliable than holding a handset up to your laptop speaker.

What you can use it for

Useful for testing a phone line or a softphone, debugging an IVR or voicemail menu that listens for key presses, and checking that a recording carries the tones cleanly.

Debugging an IVR or a voicemail menu. Dial the digits by hand while you watch the system react, then dial the same string as a sequence to check that it still decodes at normal telephone speed.

Testing a softphone or a conference bridge. Playing tones into the microphone shows whether the far end accepts in band DTMF at all, which is worth knowing before you blame the menu.

Checking that a recording survives. Dial a sequence into a recorder or a codec chain and play it back: if the tones no longer decode, the compression, the noise suppression or the sample rate is destroying them.

Radio and equipment control. DTMF still opens repeaters, selects channels and triggers remote gear, and a browser pad is a quick stand in for a handset when you are bench testing.

Where the touch tone keypad came from

DTMF, short for dual-tone multi-frequency, is the signalling a telephone keypad uses: each key sends one low row tone plus one high column tone at the same time.

Bell Labs worked out the scheme in the 1950s and AT&T put Touch-Tone dialling in front of the public at the 1962 World's Fair, with service starting the following year. Two tones per key was the clever part: no whistle, no voice and no single stray tone on the line can fake a digit.

The eight frequencies were picked so that none of them is a harmonic or a simple sum of the others, which keeps speech and music from accidentally producing a valid pair. That is also why the tones sound so oddly dissonant next to each other.

The fourth column, A, B, C and D on 1633 Hz, never reached household telephones. It carried call precedence on the military Autovon network and still appears in radio and test gear, which is why a full sixteen key pad has it.

Accuracy and limits

A speaker and a microphone are a poor path for signalling tones. Room noise, speaker distortion and the automatic gain control in a phone or a headset all degrade the pair, and a menu that decodes perfectly over a cable may refuse the same tones held up to a laptop. Feed the audio in directly whenever you can.

Modern calls often do not carry DTMF as audio at all. VoIP systems usually send key presses as separate signalling events rather than as sound, and low bitrate codecs distort in band tones enough to break them. A system can ignore what you play even though the tones themselves are exact.

The pad plays fixed telephone timing and nothing else. There is no adjustable tone length, no pause character, no level control and no export: the sequence runs at 70 ms on and 70 ms off until you stop it.

Frequently asked questions

What does DTMF stand for?

Dual-tone multi-frequency. Dual tone because each key sends two sine tones at once, multi-frequency because the set covers eight frequencies in four rows and four columns. Older telephone people call it Touch-Tone, which was AT&T's brand name.

What are the frequencies behind each key?

The rows are 697, 770, 852 and 941 Hz and the columns are 1209, 1336, 1477 and 1633 Hz. A key is the sum of its row and its column, so 1 is 697 plus 1209 Hz and the hash key is 941 plus 1477 Hz.

Why does the phone menu not recognise my tones?

Usually the path rather than the tones. Acoustic coupling through a speaker and a microphone loses too much, and many VoIP calls carry key presses as signalling data rather than audio. Try a direct audio route, and dial the digits one at a time.

What are the A, B, C and D keys for?

They are the fourth column at 1633 Hz. Consumer phones never had them; they were used for priority levels on the military Autovon network and survive in radio control, test equipment and a few automation systems.

Can I dial a real number by holding my phone to the speaker?

Sometimes, on an analogue line and in a quiet room. It is unreliable on a mobile or a VoIP call because of noise, compression and the way key presses are signalled, so treat it as a test rather than a way to place calls.

Does the dial pad work offline?

Yes. The tone pairs are generated by the Web Audio API on your own device, so once the page has loaded you can disconnect the network and every key still sounds.