What's the difference between an analog and digital modem? reddit / bbs ---------------------------------------------------------------------- US-Robotics · 2023-02-13 13:01 Up until recently, I was under the impression that a modem, one that does the noises and beeps over a telephone line, is an "analog modem". Then I read somewhere, that faster modems, V.90 etc., are "digital modems". Huh? Don't these still do analog beeps and noises over a land line? So what's the definition here? Are there two partially overlapping concepts of a modem, perhaps? On one hand, people that speak of "what a modem does" and on the other "people who mean how the modem is implemented"? I could imagine that more modern modems, the faster ones, the V.90 etc. ones, synthesized these "noises" digitally, while older modems produced noised using analog chips... Is something like that where the confusion comes from? At least, my confusion is complete... Can someone shed some light? ---------------------------------------------------------------------- aleigh9812 · 2023-02-13 20:55 To make V.90 work, one end was supposed to be the analog modem (most likely the customer end), and the other end was supposed to be a "digital modem", most likely the service provider side. What they mean by digital modem in this context is that the analog (bleep bloop) conversion to digital (like digital audio on a CD) would already have occurred in the phone network. Note that they don't mean digital like the data - they mean digital like a digital audio recording of the bleeps and bloops. This basically just takes advantage of the fact that the phone company was going to convert the signal to digital anyways, so there is no reason to take that digital signal, convert it back to analog, just so the far-end modem can take that analog signal and convert it yet-again to digital for processing. By getting rid of that redundant conversion and the associated losses they were able to eek out a bit more performance. ---------------------------------------------------------------------- dmine45 · 2023-02-13 22:08 Yep, preventing one side of the analog to digital and back to analog. The second side remains digital (on the ISP side). So for BBSes we'll never see this unless you run full digital to a modem bank, like an ISP does. ---------------------------------------------------------------------- Substantial-Bit-1915 · 2023-02-13 22:29 [https://www.itu.int/rec/T-REC-V.90](https://www.itu.int/rec/T-REC- V.90) Go to the very last page of the PDF (41) and it has a drawing of it. The others have described it well - if you want the raw nerdy details, see ITU link above. ---------------------------------------------------------------------- US-Robotics · 2023-02-14 13:26 Now it's clear. Thank you for this great explanation! ---------------------------------------------------------------------- US-Robotics · 2023-02-14 13:26 Thanks! ---------------------------------------------------------------------- US-Robotics · 2023-02-14 13:27 This document. Phew... Reminds me of how deep the science behind all this actually is. Great link.