AudioTestPro

DTMF tone generator

Telephone keypad tones on demand. Tap a key, type on your keyboard, or play a whole sequence with precise timing.

Volume first. Turn your device volume down before pressing play, then raise it slowly. Tones start quiet on purpose. Keep headphones off your ears until you know how loud it is.

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Row and column frequencies in Hz light up for each key. The highlighted pair is exactly what an exchange listens for.

0 dBFS is the loudest your device can play; every 20 dB lower is a tenth of the amplitude.

The DTMF frequency table

1209 Hz1336 Hz1477 Hz1633 Hz
697 Hz123A
770 Hz456B
852 Hz789C
941 Hz*0#D

None of the frequencies is a simple multiple of another, which keeps harmonics from one tone from being mistaken for another key. ITU-T Q.24 specifies that receivers should accept tones within about ±1.5% of nominal and reject those more than 3.5% off.

Using DTMF tones

  • Phone menus (IVR): hold a phone near the speaker to send digits when a keypad is not handy.
  • Radio and repeater control: many amateur radio repeaters and remote switches accept DTMF commands.
  • Testing decoders: vary tone length and gap to find the shortest timing your decoder accepts.

Questions people ask

What is DTMF?

Dual-Tone Multi-Frequency signalling is the system behind telephone keypad tones. Each key sends two sine waves at once, one from a low "row" group and one from a high "column" group. It was introduced by Bell System in the 1960s as Touch-Tone and is standardised in ITU-T Q.23.

Why does each key use two tones?

Two tones from separate groups are very unlikely to occur together in speech or music, so the exchange can recognise a key press reliably without being fooled by voices on the line.

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

A fourth column at 1633 Hz, used on some military (AUTOVON) and radio systems for priority and control signals. They rarely appear on consumer phones.

Can I use this to dial a phone or test an IVR?

You can hold your phone to the speaker to send tones into a call menu or test a DTMF decoder. Use a tone length of at least 100 ms with a similar gap, which the settings below provide by default.

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