I'm preparing a seminar that will take place tomorrow (4 May),
it will involve live mixing of surround sound using Ardour.
While setting up the PC to be used, two problems occured.

The first one is solved, but its cause remains misterious.
A some point it appeared that the sound card (HDSP-MADI,
used every day since years) had decided to meet its creator.
Every program trying to access it - from jackd to aplay -L
not only blocked, but turned out to be impossible to kill.
Replaced the card - same result. It turned out to be a
corrupt /var/lib/alsa/asound.state. The systemd service
doing the 'alsactl restore' while booting choked on it,
blocked, and  this apperently blocked all others trying
to use the card later. What I don't understand is how alsactl
exactly failed, and why these processes seemed to be immune
to a 'kill -9'.

The second one is an Ardour2 session that worked perfectly
on another similar PC, but becomes completely unresponsive
on the one to be used. It has four mono tracks and three
10-channel ones, and little else. DSP load is not the problem,
it's less than 15%. Things look like it's the graphics. When
Ardour's playhead reaches the right end of the editor window,
it takes something like 5 seconds for the editor display to
update - everything seems to freeze during that time but audio
is not interrupted. Same when trying to scroll or change the
zoom factor. Video card is Nvidia GeForce 7300, indeed quite
old, but the same PC does full-screen HD youtube videos without
problem. Video driver is nouveau as nv seems to be no longer
supported by Archlinux. I'm pretty sure this system didn't have
such problems when it was using nv. OTOH nouveau works very well
on other systems... I could try and install the proprietary
Nvidia driver, but with just some hours to go I'd rather not
take any risks...

Any hints ?

Ciao,