I understand that modems used the telephone line to transmit and decode sound into data, but I don’t understand why that noise everyone remembers needed to happen. You didn’t hear sound when you were loading a web page even though sound was being decoded by you modem… what was the purpose for it on start-up?
Edit: Autocorrect typo
In: Technology
That sound was the same as what was transmitted on the phone line during dialup. It’s the two modems exchanging data about each other and the connection and if you knew what to listen for you could detect if something was wrong just by what part of the sound was not as it should be.
To add to what the others have written: in the earlier days of modems (e.g., when modems were 300 baud), there wasn’t any negotiation. The far end was simply what it was: you just had to know what its setting were.
On the one hand, this makes the connection setup time essentially zero time (other than dialing!). On the other, you had to know what the other side was supporting.
The modems were testing the phone line, negotiating with the other modem on what protocols to use and how to work around noise on the lines. The sounds does sound very similar to us humans but to the modems even a small change in the pitch in one of the tones changes the meaning completely. And as the modems negotiate to higher and higher speeds it will sound more and more like static noise to us.
It’s because there were a lot of different speeds of modems, based on the capability of the modem itself and how good the connection was.
Think of it like someone who can speak many languages calling in to a customer service line. He’d probably start with the language he’d assume is used: “Hi, this is Mr. Polyglot, my printer stopped working.”
If he hears a “uh…” on the other side: ok! Not English; he needs a different protocol for them to understand him.
“Sprechen Sie Deutsch?” “…”
“Habla Espanol?” “…”
“Nihongo wa hanasemasu ka” “Hai! Nihongo desu!”
Protocol established! They speak Japanese! Now Mr. Polyglot knows he will need to speak Japanese in order for them to understand his question and send an answer.
The connection matters as well. It doesn’t matter if you can send and receive data super fast if most of it is garbled by the time it gets there! If Mr. Polyglot has a bad connection, even if he is speaking the language they understand — the right protocols to connect — half or more of what they say to each other is garbled. So, during that first exchange of greeting and response, they’ve also figured out how slowly they need to talk to help the other person understand.
Good connection? Both people can talk fast (if they can). Bad connection? They will probably slow down and talk more carefully so they don’t have to repeat everything fourteen times.
The noises you hear are basically: HI! I’m a 56.6K modem! …you’re not? Hi! I’m also a 28.8K modem! Great, you are too! Crap, our telephone connection sucks, though, how about we drop to 14.4K … testing…. testing… now you hear me fine? Great! Ok, here’s what I wanted….
It was audible back then as a way to troubleshoot what was going on. As rarely as that was used. Not sure I ever knew anyone who did.
There were many standardised signals in the first part of the connection. By the time you’re sending particular data, it’s mostly noise to the human ear (which the modem usually silenced, but you could turn it on if you wanted – it just sounds like Sssssshhshshhshshshshhshshshshshhshs).
But the first parts are tones to indicate “I’m a computer, not a person” (to stop faxes and automated systems getting confused by not having a voice), then a response to say the same from the other end, then a serious of small data blips, then a long wavering/diminishing sound as the two sides negotiated speeds and discovered whether there was any interference on certain frequencies. Then it’s mostly static but sometimes you would hear a sudden sssshshshshhshsNNNNNNNNNEEEENNNNNNNNNAAAANNNNNNOOOONAAAAAAshshsshs – that usually indicated that the two sides had lost communication briefly, and they letting the other side know so they could both start again (or downgrade the speed slightly next time).
Growing up with a ZX Spectrum gave you a fine ear for what was happening in an audio-based data stream…
The sound was not the same. I worked in dial up tech support and you could tell a lot by listening to the modem.
You had the option to turn it off, but it was left on by default to let you hear what was going on. You could tell the modem speed and protocol by what the sounds were doing before they stop.
When you start your car, all the lights on the dashboard light up before you turn the engine over. This shows you the electrical system is working, and allows you to check each individual light is working even if its specific fault is not present (i.e. you can diagnose if it’s the bulb faulty, or an genuine fault). By making the noise during dial-up you can hear that something is happening, i.e. you can hear that your end and the other end are making some sort of connection. You can’t understand what they’re saying to each other, but you know they’re talking. If there was no noise, you wouldn’t know if they were talking or if you were dialling a dead number, or you’re line was faulty. Once connected the noise turns off as you really don’t want to continue hearing anything.
The sounds that you hear at the two modems discovering each other, and agreeing on the speed to communicate at. The calling modem tries at the highest speed it can go, then retries at slower and slower speeds until the both modems are happy with the speed and the sound quality.
The only reason you can hear the sounds are so you can tell if the connection working. You can tell if a human picked up the phone, or if the line was busy, or never picked up. You will recognize that and do something about it faster than waiting for the connection timeout.
Once the connection is established the speaker is turned off – the sound still continues on the phone.
The audible tones were there to establish the connection between the modems on both ends. After the “handshaking” between the modems, your pc modem muted its speaker.
The speaker was turned on during dialing so the person on the computer could hear if there was dial tone, if someone was already on the phone or there was a busy signal.
In the 80s, most homes only had one telephone line which was shared between the pc and all the other telephones in the house.
All the different parts of it have a definite purpose. It’s the two modems at each end figuring out what each others causalities are and how good the line is.
The best description I ever saw [is visual…](https://oona.windytan.com/posters/dialup-final.png)
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