Interesting interview; thank you for doing it. Here's a few questions.
You say that for end users, ALSA just works, and you tend to encourage it for newbies. What are the tradeoffs? What kind of latency penalty am I taking by using ALSA vs JACK? Can it scale to as many channels?
What's your preferred JACK frontend? The UbuntuStudio UI has some nice bridging set up out of the box, so you can e.g. play Youtube while Ardour or Reaper is active. QJackCtl certainly works (and offers a UI around the patchbay you describe) but it doesn't have that feature at least.
Does Pipewire aim to solve the problem of persistent device names? I had a bit of an adventure figuring out how to set up ALSA so that it didn't constantly give new numbers to my audio interface, USB midi IO, control surface, etc (which was painful, because it meant having to reconfigure the DAWs after each reboot.) Once I found the right howto, it wasn't too bad, but it'd be nice if that was taken care of.
Do you have any background knowledge on Bitwig's weird MIDI setup? They support JACK audio, but not JACK midi, so you have to do this weird juggling act to bridge midi to ALSA, which was too much friction for me to bother with (and so I don't use Bitwig.)
Finally, is there much difference between audio interfaces in terms of latency as long as they are USB class compliant? If there is, are there any good references that you know of? Or is it a case of experimentation?
ALSA vs. JACK: there's no latency difference at all. There is a very tiny decrease in CPU load from using ALSA directly (no context switching between the JACK server and clients). No difference in channel counts. Note also that my recommendation was within the context of Ardour: use Ardour's own ALSA audio/MIDI backend, rather than it's JACK audio/MIDI backend (unless you actually need JACK-like capabilities).
We have had users complaining about Ardour in the context of Bitwig's wierd MIDI, indeed. I've never spoken to anyone involved in Bitwig development. I could make guesses about why they did what they did, but they would just be guesses. It is certainly less than ideal.
USB audio on Linux sadly incurs an extra latency penalty due to a kernel-side buffer whose size varies every time the device is opened/started. This means that you will not see constant latency numbers for any USB audio interface on Linux (there are some attempts being made to fix this). However, other than that, they are all functionally equivalent, certainly from a latency perspective. I would give MOTU's recent devices a shout out purely because they've done all device configuration (the "device panel") via a web browser, and thus removed the one barrier that exists for a number of devices on Linux - the audio/MIDI side works, but you cannot configure it since that requires a dedicated Windows/macOS tool. MOTU were the first company I know of to do this, and despite their virulently anti-Linux attitude in the past, it really makes Linux a first class platform for their newer devices (ignoring a few SNAFUs with the firmware, unfortunately).
You say that for end users, ALSA just works, and you tend to encourage it for newbies. What are the tradeoffs? What kind of latency penalty am I taking by using ALSA vs JACK? Can it scale to as many channels?
What's your preferred JACK frontend? The UbuntuStudio UI has some nice bridging set up out of the box, so you can e.g. play Youtube while Ardour or Reaper is active. QJackCtl certainly works (and offers a UI around the patchbay you describe) but it doesn't have that feature at least.
Does Pipewire aim to solve the problem of persistent device names? I had a bit of an adventure figuring out how to set up ALSA so that it didn't constantly give new numbers to my audio interface, USB midi IO, control surface, etc (which was painful, because it meant having to reconfigure the DAWs after each reboot.) Once I found the right howto, it wasn't too bad, but it'd be nice if that was taken care of.
Do you have any background knowledge on Bitwig's weird MIDI setup? They support JACK audio, but not JACK midi, so you have to do this weird juggling act to bridge midi to ALSA, which was too much friction for me to bother with (and so I don't use Bitwig.)
Finally, is there much difference between audio interfaces in terms of latency as long as they are USB class compliant? If there is, are there any good references that you know of? Or is it a case of experimentation?