[LAD] JACK latency compensation on USB audio devices

Joakim Hernberg jhernberg at alchemy.lu
Wed Sep 2 19:04:23 UTC 2015

I've run across a phenomena that puzzles me.

It appears that each time I start the jack server on an usb card,
jack_iodelay will report a different "extra loopback latency".  I've
seen this phenomena on a behringer x32, and just verified it on a rme

For instance with jack1 at 64/2 on the babyface, I come up with values
of 232,233,234, and 266.  With jack2 I saw 231, 233, 248, 318, 335. A
run with jack1 at 2048/3 came up with 2589, 2590, 2633, 2634, and 2667.

I also tested with jack_delay, which also comes up with different
values when I restart the server.  Note that on consequent invocations
without restarting the server the values stay the same for the 2

Maybe not a huge problem and I suppose I'll set the latency
compensation somewhere in the middle of the results, but still I'm
curious of the mechanism behind this phenomena.

FWIW, I don't think I've ever seen this on my pci cards, but I'll run
some tests when I get to the hardware and find some extra time.



More information about the Linux-audio-dev mailing list