[Jack-Devel] advice on xruns

Robin Gareus robin at gareus.org
Sun Jul 28 17:41:14 CEST 2019

On 7/28/19 5:26 PM, liebrecht at grossmann-venter.com wrote:
> I get 2-10 xruns in the brackets, when I just start up, probably while
> starting jack etc.
> After Mixbus is started and up, it stays at that value for hours as far
> as I tested which is supernice

That is indeed awesome.

And yes, while loading sessions, Mixbus can skip a few cycles, until
caches are warmed up, etc.

Also keep in mind that some operations are inherently not realtime safe.
e.g. adding/removing jack-ports (e.g. add/remove tracks in Mixbus).
Changing connections or adding/removing plugins may also cause
additional DSP spikes.

But those are edge-cases. It's not something one does while recording or
when mixing live with low-latency.

> I just wish I could work at 48000Hz.

I use the VSL1818 at 48kHz exclusively. I still have a 8+ year old
original firmware (and I have to force USB3 ports to USB2 compat).

I heard that some people have issues once the device as at least once
connected to a Mac or Window box. Maybe a factory reset can help?

> Maybe I dont understand alsa correctly, because a 48kHZ jackd string
doesnt work at 48kHz.

That's jackd's fault. Jack's ALSA backend always silently falls back the
"closest available" samplerate. -- IMHO it should rather fail instead,
but it doesn't.

You can check with the `jack_bufsize` commmandline tool. That prints the
actual current buffesize and samplerate.


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