[throwaway67743]

You want 722 really, one of the choices for "HD voice", it mangles it much less than even 711

[lxgr]

No, unlike G.711, G.722 is lossily compressed using psychoacoustic concepts, and modems wouldn’t know what to do with the extra acoustic frequencies anyway.

G.722 might sound better to humans, but G.711 is definitely better for modems since it’s effectively just uncompressed PCM (disregarding a bit of dynamic range compression which modems are generally fine with).

[throwaway67743]

It is compressed, yes, but at higher bitrates it is actually usable for modems/faxes, you're limited to low baud rates anyway due to jitter and sample intervals. But really the benefit is 16k sampling rate instead of 8, I'm not saying it's great but it's the best we've got.

It would be possible to mask this with a relatively simple FXS device to hide all of this and pretend it's a modem while packetising the actual data, but I guess the demand is almost zero so why bother.

I've been looking for a solution for many years to retain dialin services without having racks full of modems and trunks that are rapidly going out of fashion and at some point will not be available except via IP (and now we have the same problem at both ends), but they just don't exist.

[ssl-3]

Have we forgotten about T.38[1]? It is designed just to let analog fax machines/modems send documents over IP.

1: https://en.wikipedia.org/wiki/T.38

[wolrah]

G.711 is what's used on the actual PSTN, so there's not even a hypothetical benefit from G.722 unless you're going direct over IP to another host supporting 722, and if you're doing that then you're probably better off with T.38 or just dropping the modem entirely for serial-over-IP.