3.5mm jack audio quality?

[wibble]

Pinephone uses the built in headphone output of the A64 via a BCT4717 analog switch chip between it and the headphone socket to switch it between headphone and serial port use. The closest I've seen to measurements is this thread, which started with some measurement errors, and lacked sufficient detail of things like mixer settings to be sure the final result was representative.
https://forum.pine64.org/showthread.php?tid=11625

I haven't checked the Pinephone Pro schematics, but you'll find the link in the wiki.