> It is over 6Kbps Opus[1].

The overhead from packet headers to send data every 40ms is 9.6kbps, is the difference between 12.6Kbps and 17.6Kbps meaningful at that point? We are sending the same number of packets, likely with the same packet loss rate.

> A RaspberryPi Zero will provide more than sufficient power for Lyra

A Raspberry Pi Zero can't run Lyra, as the proprietary math kernel is only offered in compiled form for x86-64 and android-arm64: https://github.com/google/lyra#license

> is the difference between 12.6Kbps and 17.6Kbps meaningful at that point

It is when you are sending video as well. One of the stated purposes of this work is to enable video conferencing over 56Kbps dial up modems.

> A Raspberry Pi Zero can't run Lyra, as the proprietary math kernel is only offered in compiled form for x86-64 and android-arm64

How annoying! Still - the point is that hardware capability isn't likely to be the issue.

> > You can buy a Grandstream HT802 analog telephone adapter for ~$30 and its DSP can decode Opus today

almost entirely irrelevant if you're making calls to or from the PSTN, since your SIP trunking provider most likely only supports G.711 alaw/ulaw, or even if they support you handing them a call as G.722 or any other codec, their upstreams almost certainly don't support anything other than G.711.

Isn’t the Pixel 2 much more powerful than a Raspi Zero?