Telephone Tones
A source of innocent merriment!
(W.S. Gilbert)
This page contains definitions of call progress tones
and other tones used in the British telephone network.
Call Progress Tones
These are what you hear as a calling is being connected (e.g. dial tone,
ringing tone).
The source of the following information is:
- R.S. Brown, ``A new method of tone identification'', Post Office
Electrical Engineers' Journal 71(2) 117-121 (1978).
``On'' and ``off'' durations are in ms.
The frequency is 400 Hz, except where noted.
By clicking on the [AU] ``button'', you can hear a 12-second
audio sample of the tone (if you have the appropriate hardware).
Technical note: The audio is not stored here; it is generated each time you request it,
by a cgi (Common Gateway Interface) program. The source code of the program
is here. New - code now in C++!
| | | On | Off | On | Off | Notes
| Audio sample
|
| BT | Busy tone | 375 | 375 | | |
| [AU]
|
| EET | Equipment engaged tone | 400 | 350 | 225 | 525 | 1
| [AU]
|
| RT | Ringing tone | 400 | 200 | 400 | 2000 | 2
| [AU]
|
| NU | Number unobtainable | Continuous |
| [AU]
|
| PT | Pay tone | 125 | 125 | | | 3
| [AU]
|
| DT | Dial tone | Continuous | 4
| [AU]
|
Notes
- The amplitude of the 225ms tone is 6dB higher than that of the 400mS tone.
This is specified (I'm reliably told) in BS 6305 (1992). I'm grateful to
Nigel Roles <ngr@symbionics.co.uk> for pointing this out.
- Frequency: 400+450 Hz.
- Not used any more. This really belongs in the history section!
- Frequency: 350+450 Hz.
Warbles
If all you want is a sample of a ringing (warbling) telephone so you can annoy your colleagues,
there are two, slightly different, such samples here.
Try setting them off in parallel, for an authentic ``busy office'' sound!
There is no standard for ``warbles'' (so far as I know). A warble is defined by the
frequencies of the two alternating tones (f1, f2),
and the warble frequency (fw), specified in Hz below.
In a real telephone, these values depend on the particular ringer chip used.
| | f1 | f2 | fw
| Audio sample
|
| Warble Sample 1 | 1500 | 1700 | 8
| [AU]
|
| Warble Sample 2 | 900 | 1100 | 8
| [AU]
|
Dual Tone Multi Frequency
DTMF tones are used for ``dialling'' a number. Each digit is signalled by a 100ms
burst of f1+f2 Hz, followed by 100ms silence. Some equipment will accept shorter
pulse durations, or shorter silent durations, but this is not recommended.
The frequencies f1, f2 are given by the following table.
| | 1209 | 1336 | 1477 | 1633
|
| 697 | 1 | 2 | 3 | A
|
| 770 | 4 | 5 | 6 | B
|
| 852 | 7 | 8 | 9 | C
|
| 941 | * | 0 | # | D
|
E.g. digit `5' is signalled by 770+1336 Hz.
Enter a string of digits from the set { 0-9, *, #, A-D } in the space below
for a sample.
Here's some C++ code for generating DTMF tones,
and here's some code for recognizing them.
Tony Fisher / fisher@minster.york.ac.uk