What are the tones for telephone numbers?

[WarmNPrickly]

What are the tones for telephone numbers? Are they universal or do different phone companies have different tones? When did the tones get decided on and why? What about the dial tone? Is that universal?

[Shagnasty]

They are pretty standard at least in the U.S. On many systems, it is actually the tones that are doing the communication. You usually have to press the buttons to generate the tones.

However, there are tools and web sites that will generate the tones for you and you can dial the number by holding the mouthpiece up to the speaker.

Here is one:

FreeUK - Customer information

There are also tools that let you analyze tones that are recorded like those you here generated on TV phone calls and they can tell you what the number is.

[Shagnasty]

I just used that site to dial a number via computer speaker and it works like a charm. I have heard of people that can generate them by voice but that seems pretty tricky.

[Q.E.D]

The DTMF toneset is standard. It comprises 8 different tones, two of which are sent simultaneoulsy to represent one of sixteen different characters:

  	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

[Arjuna34]

From Wikipedia:

The tone frequencies, as defined by the Precise Tone Plan, are selected such that harmonics and intermodulation products will not cause an unreliable signal. No frequency is a multiple of another, the difference between any two frequencies does not equal any of the frequencies, and the sum of any two frequencies does not equal any of the frequencies. The frequencies were initially designed with a ratio of 21/19, which is slightly less than a whole tone. The frequencies may not vary more than ±1.5% from their nominal frequency, or the switching center will ignore the signal. The high frequencies may be the same volume or louder as the low frequencies when sent across the line. The loudness difference between the high and low frequencies can be as large as 3 decibels (dB) and is referred to as “twist”.

Basically, the specific frequencies were picked to make it as easy as possible for automatic equipment to reliably distinguish any pair.

Arjuna34

[Richard_Pearse]

@Christopher

What about the dial tone? Is that universal?

The dial tone is not universal by country at least. In Australia it is something akin to a high pitched cat’s purr, in New Zealand it was a steady ‘G’. This was very handy for tuning a guitar when no tuner was near by.

[lskinner]

I knew a guy who could dial a phone number just by humming. He mainly used it to pick up chicks.

He could also get free phone calls from pay phones. It was pretty amazing.

[CookingWithGas]

@lskinner

I knew a guy who could dial a phone number just by humming. He mainly used it to pick up chicks.

He could also get free phone calls from pay phones. It was pretty amazing.

The legendary Joe Engressia.

[HMS_Irruncible]

@CookingWithGas

The legendary Joe Engressia.

Whistling a single 2600 tone is not that hard, it only requires a memory of that pitch. But I have to call BS on any story of someone who claims to have “whistled” keytones, which as mentioned before are a combination of 2 tones.

[lskinner]

This guy used humming not whistling. Maybe that makes a difference. But you’d hold the phone up to him while he held his hands behind his back. A girl would give him her phone number and he would hum a little and tell her to take the phone – it would be her message machine picking up. And he would have her phone number. Pretty slick.

[Bytegeist]

@Q.E.D.

The DTMF toneset is standard. It comprises 8 different tones, two of which are sent simultaneoulsy to represent one of sixteen different characters:

  	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

*… Thank you for calling Capital One. Your call is important to us … To hear your current balance, press “1”. To make a purchase with your Miles One points, press “2”. To speak with a customer representative, press the “B” key …

Don’t have a “B” key, do you kiddo? Well that’s just tough t*tties to you then. No customer representative for you, you and your little twelve-key wonder there. What is that anyway — Baby’s First Phone?

To hear this menu repeated, press the “star” key …*

[parabolis]

@Brain Wreck

I have to call BS on any story of someone who claims to have “whistled” keytones, which as mentioned before are a combination of 2 tones.

QED provided a link in another thread recently to a page that describes the sine wave. At the bottom of the page are examples of synthetic vowel sounds. The third example is ‘a’ which is synthesized by combining the frequencies 100 Hz, 700 Hz and 1300 Hz. The 700 Hz and 1300 Hz components are very close to the 697 Hz and 1336 Hz required to dial 2. So it seems quite likely to me that somebody willing to spend the time training should be able to dial by humming.

[Sunspace]

:: dredges up memories of electronics school ::

The A, B, C, and D tone-combinations were intended only for the US military and government. IIRC, they indicated a higher-priority call, and would cut through other traffic if there was no line free. The buttons were given exciting 1960’s Cold-War names like “Flash” and “Flash Override”. I don’t know whether this applied only to military phone systems or to the entine US civilan system as well.

Wikipedia on DTMF:

The engineers had also envisioned phones being used to access computers, and surveyed a number of companies to see what they would need for this role. This led to the addition of the number sign (#) and star (*) keys, as well as a group of keys for menu selection, A, B, C and D. In the end the lettered keys were dropped from most phones, and it was many years before the # and * keys became widely used, primarily for certain vertical service codes such as *67 in the United States to suppress caller ID. Many non-telephone applications still use the alphabetic keys, such as amateur radio repeater signaling and control (see also autopatch).

Public payphones that accept credit cards use these additional codes to send the information from the magnetic strip.

The U.S. Military also used the letters, relabeled, in their now defunct Autovon phone system. Here they were used before dialing the phone in order to give some calls priority, cutting in over existing calls if need be. The idea was to allow important traffic to get through every time. The levels of priority available were Flash Override (A), Flash (B), Immediate ©, and Priority (D), with Flash Override being the highest priority. Pressing one of these keys gave your call priority, overriding other conversations on the network. Pressing C, Immediate, before dialing would make the switch first look for any free lines, and if all lines were in use, it would hang up any non-priority calls, and then any priority calls.

Present-day uses of the A, B, C and D keys on telephone networks are few, and exclusive to network control. For example, the A key is used on some networks to cycle through different carriers at will (thereby listening in on calls). Their use is probably prohibited by most carriers.

Phone sets with the extra buttons.

[CC]

@Brain Wreck

Whistling a single 2600 tone is not that hard, it only requires a memory of that pitch. But I have to call BS on any story of someone who claims to have “whistled” keytones, which as mentioned before are a combination of 2 tones.

I saw an article on the guy on tv a number of years ago. He may have been whistling and humming at the same time - you can do that, of course, and you can whistle one tone and hum a different one. Try it. Fact is, he did it and clearly got the phone system to respond. Not BS.

[Roland_Orzabal]

I just called my office VRU, and tried humming the touch-tone options at it, using the site linked above as a guide. It worked. Haven’t tried it with a dialtone yet…that may well be trickier.