Old telephones actually had a bell that rang when they received a call. New phones just play a digital recording.
What makes the ringing noise the caller hears in the receiver? I think these days we call it the “ringback” tone. Was it originally the bell from the phone on the receiving end?
The ring tone* is generated by the central office serving the number you’ve dialed. It’s an acoustic signal, vs the (usually) 90 volt, 20 Hz ringing signal that’s put onto the called line.
Some of ‘em still work, freakin’ decades after they were really useful.
A real '80’s Bell touch tone phone can still be a lot of fun to play with.
As others have said this tone is generated by the Telco switching equipment. After the days when all calls were completed by an operator, phone switches evolved through several methods of automation.
First came rotary phones, and step by step switching. When you dialed a number on the rotary phone, the mechanism inside the phone generated electrical pulses which were used to route your call. You dial an 8 for instance, and eight pulses are sent down the line. Imagine every number in a telephone switch existing in a large series of circuit banks. You dial 555-1212 on your rotary phone, and this causes the mechanism within the switch to select bank five. Bank five has ten banks that can be selected. Your next digit is another five, so select the fifth connection from there, which routes you to the next bank of circuits by the fifth connection in the current bank. And so on. The pulses of your rotary phone were physically guiding the electromechanical switch to route your call. Note that back then the first two digits of the number represented the specific local office you were connecting to. The old style numbers like “hopkins 3-6099” were converted to 7 digit numbers, which is why we have the letters on our phones today. HOpkins exchange would become “46” for HO and the above number becomes 463-6099.
The phone system then evolved toward DTMF, or dual tone modulated frequency signalling. This is where touch tones come from, as well as the ringback tone. As switching equipment became smarter, and the phone system grew, there was no longer a need to for your phone to physically guide the switch toward the correct circuit to complete your call. New technology enabled the switch to recognize special frequency combinations rather than the electrical pulses of rotary dialing.
These tones largely consist of two-tone DTMF pairs. This is where we got the familiar touch tones, dial tone, ringback tone, busy signal, etc. IIRC the ringback tone consists of a 440 and 460 Hz pair.
Note that most of the above is from memory of a phone system obsession I had many years ago so may be factually incorrect a bit but hopefully is conceptually sound.
If you would like to know how the specific frequencies were determined I defer to Wikipedia’s article on DTMF:
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I far as I know, and I have some decent telephony info, the two signals were never the same. Certainly during the touch-tone era this was the case. I’m sure many of us can recall instances where the caller picks up before you get in your handset a ringback tone. The central office is sending out non-synchronized ring and ringback tones.
I can remember the same phenomenon happening back with rotary phones being the only kind around: The sort of magical way, it seems, that your called person can pick up without the phone ever ringing. In the human operator system the operator would note your desired number and ring them separately while you were on the line with the operator.
If you’re trapped on top of an Aztec pyramid in rural Mexico by crazed locals, it’s caused by plants vibrating their stamens.
My Uncle who worked for the phone company in the 80’s said, “it’s called the Ring Machine.” An electronic device of some sort in the telephone company building.
As others have said, in analog systems, the ringback is generated by the CO. However, it may or may not be the local CO. This accounts for the case where your ringback changes while you are waiting or in the case of international dialing where your ringback is the kind used in the called country. It all depends on the type of equipment linking the caller and callee.
Even new VoIP phones have the ability to play ringback locally (by generating the tones internally) or to play the ringback generated remotely and sent over the audio channel. While generating ringback in the CO (PBX, etc.) and sending it over the audio channel is a waste of CPU and bandwidth, it allows the CO to control the ringback tones (playing international tones for instance) or even dispense with the ringback tone and to play recorded audio instead (this is often called Early Media).
To be specific, in the US, the Audible Ring Tone is 440 Hz and 480 Hz for 2 seconds on then 4 seconds off at -13 dBm0/frequency.
I used to have a phone that would make a single ding! when a call connected, before it started ringing properly. I would always amaze people with my ability to pick up the phone before it rang.
So you can rescue yourself by shooting them with your pistil? :o
Pervert herbisexuals… 