What each tone means
- Dial tone:
- The exchange is ready for you to dial.
- Busy signal:
- The number you called is engaged.
- Ringback:
- The other phone is ringing.
- Reorder / fast busy:
- The call could not be routed: the network, not the person, is busy.
- Off-hook howler:
- A handset has been left off the hook.
- SIT (intercept):
- Three rising tones before a recorded message, such as "the number you have dialled is not in service".
- Call waiting:
- Another call is arriving while you are on the line.
Frequencies and cadences by region
| Tone | US | UK | EU | JP |
|---|---|---|---|---|
| Dial tone | 350 + 440 Hz Continuous | 350 + 440 Hz Continuous | 425 Hz Continuous | 400 Hz Continuous |
| Busy signal | 480 + 620 Hz 0.5 s on, 0.5 s off | 400 Hz 0.375 s on, 0.375 s off | 425 Hz 0.5 s on, 0.5 s off | 400 Hz 0.5 s on, 0.5 s off |
| Ringback | 440 + 480 Hz 2 s on, 4 s off | 400 + 450 Hz 0.4 s on, 0.2 s off, 0.4 s on, 2 s off | 425 Hz 1 s on, 4 s off | 400 Hz modulated at 16 Hz 1 s on, 2 s off |
| Reorder / fast busy | 480 + 620 Hz 0.25 s on, 0.25 s off | 400 Hz 0.4 s on, 0.35 s off, 0.225 s on, 0.525 s off | 425 Hz 0.25 s on, 0.25 s off | not included |
| Off-hook howler | 1400 + 2060 + 2450 + 2600 Hz 0.1 s on, 0.1 s off | not included | not included | not included |
| SIT (intercept) | 913.8 → 1370.6 → 1776.7 Hz 276 ms, 276 ms, 380 ms (intercept code), then 2 s gap | 950 → 1400 → 1800 Hz 3 × 0.33 s with 30 ms gaps, then 1 s off | 950 → 1400 → 1800 Hz 3 × 0.33 s, then 1 s off | not included |
| Call waiting | 440 Hz 0.3 s beep, repeated after 10 s | not included | 425 Hz 0.2 s on, 0.2 s off, 0.2 s on, 5 s off | not included |
"Not included" means this page has no verified value for that region yet, not that the network has no such tone. The UK reorder entry is the congestion tone. Europe's call waiting is the German cadence, as Europe has no single standard one.
Why every country sounds different
Phone networks grew up nationally, each with its own equipment and its own choice of tones. The ITU recommends a general shape for these signals (a dial tone is continuous, a busy tone is evenly on and off, a ringing tone is a short burst then a longer silence) but leaves the exact frequencies and timings to each country, and publishes the list of what each one uses.
North America standardised on the precise tone plan, which builds every tone from pairs of 350, 440, 480 and 620 Hz. European countries agreed on a common 425 Hz tone through CEPT and ETSI, though many still differ in the details. The UK kept its own set, including the double ring. Because the network you are calling plays the ringing tone, you hear the destination country's ring, which is why a call abroad can sound strange.
Using telephone tones in film, video and apps
For a scene, match the tone to the setting: a 425 Hz busy signal places a call in Germany or Italy as surely as the street signs do. Download a length that covers the shot and cut it on a silence in the cadence, so the edit is invisible. A ringback under dialogue usually wants to sit well below the voices.
In apps, VoIP systems and phone menus, these files work as placeholder or test signals for call-progress detection. For the keypad sounds rather than the network tones, use the DTMF tone generator; for a single steady tone at any frequency, the tone generator.