Re: Trying to understand pipewire jack emulation better

Thank you so much for your valuable replies Chris and Orest! 

Here is a progress report on pipewire and a few questions that came up:

I have given pipewire a try by installing (on Debian stable) 
 $ aptitude install pipewire pipewire-alsa pipewire-jack rtkit wireplumber
and can use it after a reboot, for example with mpv natively.

I also found that regarding the tools
pw-cli seems overcomplicated,
pw-dump is for debugging mainly.

wpctl seems helpful setting a default device
 $ wpctl status
 $ wpctl set-default ID

and it is new and exciting for me to be (un)plugging my external usb
card and have audio shift over during playback!

pavuctl (which requires pipewire-pulse to work) is a usable graphical
interface to pipewire settings as well, as indicated by the kind posters
on this list.

Setting quantum and sampling rates with pw-metadata seems to work, but I
am confused about the difference between clock.rate and
clock.force-rate or between clock.quantum and clock.force-quantum.

So far I use this to un-set a forced value and hope it works:
 $ pw-metadata-n settings 0 clock.force-rate ''
 $ pw-metadata-n settings 0 clock.force-quantum ''

I am wondering how I can pre-set different quantums for different cards?
My external usb card seems to manage 32 fine, while the laptop's internal
card chokes on such low values and I would like to switch back and
forth between cards without having to re-set quantum every time.

Orest, you also mentioned pipewire.conf.d would this be a place to set
quantum per device? Is there any documentation you can recommend?

Is the PIPEWIRE_LATENCY environment variable honoured, and what does it
do?

pw-jack works nicely, but doesn't seem to respect pipewire's default
audio device?

It is nice that I can still start native jackd with qjackctl and
pipewire will release that card.

Also by following the advice in https://wiki.debian.org/PipeWire (Thanks
again, Chris!) and copying
 $ /usr/share/doc/pipewire/examples/ld.so.conf.d/pipewire-jack-*.conf /etc/ld.so.conf.d/
 $ ldconfig
jack applications now can use the pipewire-jack emulation by default.
However, I am wondering if I can still start native jack, since qjackctl
will now also use the jack libraries provided by pipewire, no?

I am very grateful for all ideas and hints!
best, Peter