On Wed, Oct 27, 2021 at 2:31 PM John Floren <john@jfloren.net> wrote:
On Wednesday, October 27th, 2021 at 11:17 AM, Chris Hanson <cmhanson@eschatologist.net> wrote:

> Obihai makes some decent, cheap-on-eBay, unlockable/hackable analog VoIP boxes that work just fine with not-super-fast modems. You won’t get 56K or even 33.6, but 9600-14.4K should be fine and a Telebit Trailblazer probably would be too if you want to use UUCP over dialup…
> — Chris

I've got a Grandstream HT801 through my ISP (Sonic.net) which works fine for voice, and it previously did ok with the modem, but now when I try, I start to get garbage soon after the connection establishes (see http://jfloren.net/noise.jpg for an example). It happens regardless of who I connect to, and seemingly without regard for the connection speed--although at 9600, the garbage fills up the screen quite rapidly compared to a rather sedate trickle at 4800.

My guess is that the codec it uses is optimized for human speech and gets confused by the range and levels of data modulation.

My modem-fu is rather weak, so if anyone recognizes what's going on, please let me know. I worry that it's just a noisy phone connection, but I was under the impression that modems had some sort of error-correction built in (this is a SupraFaxModem 288).

This depends very much on the modem. It might be painful, but I wonder what would happen if you tried it at 1200 or even 300 baud (assuming those are simple AFSK using two tones as in Bell 103 and 202 schemes).

        - Dan C.