[Jackaudio] Latency compensation with multiple Jack-Instances connected by zita-njbridge

[Robin Rosenberger]

Hello jack community,

I am trying to run two separate Jack instances, one for low latency monitoring using Carla as a plugin host and one for recording using Ardour with a higher buffersize for performance. The two jack servers are connected by zita-njbridge.

Its working quite well so far, the issue is that I cannot compensate for the latency of the zita-bridges, 2*10ms. To my knowledge, jack provides latency information to Ardour, so i need to inform jack about the latency happening. I tried the following setups:



Main Jack, alsa backend using USB Interface (Presonus Audiobox USB96)

Ardour Jack, dummy backend

and

Main Jack, alsa backend using USB Interface

Ardour Jack, alsa backend using onboard audio (Intel 8 Series/C220 if it matters)



Signal way in both cases for recording is:

System in Main Jack - Zita to Ardour-Jack - Ardour - Zita to Main Jack - System out Main Jack

So I never use the onboard physical connections.



The first setup is problematic because the dummy backend doesn't have extra latency options, the latter seems to be ignoring the -I -O numbers in the Ardour-Jack, at least jack_iodelay tells me the same frame count no matter what I enter, which is not the case in the Main-Jack, where I can get it to 0 with the correct settings.

So I get late recordings by 20ms from zita + the latency of the Main-Jack, that the Ardour-Jack doesn't know about.



Is there any way to make this work? And why is the Ardour-Jack ignoring my extra latency settings?



Even though I don't think it matters too much, I'm on Arch Linux, and using jack2 1.9.16-1 and Ardour 6.3-3.

Looking forward to your replies, stay safe and healthy!

Best regards,

Robin
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