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Modem Sounds Explained, Part 1: Audio Frequency Shift Keying and Bell 103
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- Опубликовано: 30 май 2022
- I've gotten a number of question on my modem sounds videos about the meanings of the sounds. This video is the first in a series that will explain their meaning, and together they'll cover the evolution of modem negotiation.
Up first, we talk about modems that don't really negotiate at all! This is Audio Frequency Shift Keying and Bell 103.
I still find it crazy how even today there's things still made that use bell 103, it's just so simple that it's hard to really break. Cathode Ray Dude did a great video on Bell 103, I'd recommend checking it out (sorry for promoting his video here)
It really is a super robust and simple way to communicate, and there are so many use cases that just don't need much bandwidth.
Also, don't be sorry! CRD's video on Bell 103 is great, and is a totally different style anyway.
I knew it had to work this way, but incredible to have you explain this so well. Finally I have some knowledge now, 30+ years after I dailed in to my first BBS with an Amiga and a 300 Baud Hayes modem. Magic!
Thanks a lot. 💜
Thank you so much for checking it out. I'm really glad it was helpful!
@@retrocet Helpful, fun and very well made. This stuff is important documentation. 👌
this! this is exactly what I've been looking for! thank you for the thorough demonstration.
Thanks for making this, it's more interesting than I thought it would be. I really find it cool how back then the frequency was actually something audible to us
I'm glad I'm not the only one that thinks it's cool :)
Modems be vibin 🎶
Amazing! I've been curious about learning in detail how dialup works recently, and then this shows up in my recommendations section, perfect timing. I especially appreciated the recordings and analysis of the actual data transfer, most videos on RUclips that I've been able to find so far only seem to cover the handshake. Very much looking forward to more! :)
I'm really glad it was helpful! I'm hoping to dig into the actual data transfer for some of the faster speeds as well - covering QAM at 2400bps I think would be really instructive. I'm going to need to source some better gear for it, but that's in the works :)
Excellent!! I look forward to the rest of this series…
The only part missing, that I'm curious about, is the notion of half/full duplex over the telephone system and how it works.
When two person speak at once, is it over 2 seperate audio canals, or are we sharing a single medium?
I'm guessnig the latter, otherwise why would Bell 103 use two different frequencies for both direction.
I guess I just answered myself. There's a shared medium, and Bell 103 is full duplex thanks to the two different frequencies.
You did answer your question for sure - they deliberately picked orthogonal frequencies to avoid cross talk, because there's lots of it in this medium. In fact for voice hearing yourself is a feature - 'sidetone' lets you hear yourself and helps people talk more naturally on the phone (it's common to kind of yell without it).
Also, this will actually end up being part of a later video in the series! Echo cancellation became very important for higher speed modems :)
@@retrocet We hear ourselves? Lol ... I never realized 😂
Is it something that was amplified/added later on? We hear all those stories about how old folks used to shout in their phone the more long distance the call was. I had always attributed it to poor amplification over long distance back in the early days.
I actually think it was _worse_ in early phones, and actually needed equipment to keep it at a reasonable level.
That said, you might still be correct about long-distance calls being quieter - it would be a natural reaction to a caller being really quiet to assume that you're also really quiet to them, and raise your voice to compensate - like yelling across a field.
love your videos on computer telephony! always well done
Excellent! Can’t wait for the next installment.
Wow!! Loving these vids man, excited to see more!
This channel is so awesome. I love these old technology. Subbed!
I playing around with making a Bell 202 compatible modem at the moment, so this is extra interesting. :)
Thanks very much for making this video.
I really enjoyed how you presented this. It’s super interesting and I’m looking forward to more from you!
Thanks very much! I'm really glad you enjoyed it!
Cant wait for part 2
That orange rotary phone looks incredible
Hi Retrocet! Do you have any interest in continuing this series? I'm eagerly awaiting the next episode :)
Hi! I do intend to continue! Life for the past year had a lot of big changes, some good, some bad, all distracting. I've started working on this stuff again though, and I'm building a better setup with higher end gear to record the tones, which will make the analysis easier and clearer.
Anyway, I'm still here!
Thats great to hear! Wish you the best, @@retrocet
What does 64, 4 and 1 stand for in 9:34 ? How do you figure them out?
we need more like this, where is part 2?
Still looking for a good collection of dial up sounds. ;) Since I lived it, its annoying to only hear that single one that everyone uses. :P
I have a few videos with a selection, but just last weekend I finally got my digital-line recording set up, with each side of the transaction in a separate channel. I'm going to start archiving sounds, and hopefully get them onto Wikipedia for reference.
Excellent video
can You explain V22 also?
Oh gosh but if I would have let’s say trying to use voice over IP and then connected on an analog line to the interconnection switch… it is not even using the IP protocol it just transmitted an H (which is the kind of thing Midjourney is still struggling with - Writing meaningful messages)…
69
nice