[LAU] Regular Xruns?

[Ken Restivo]

On Fri, Aug 07, 2009 at 02:57:56PM +0200, Arnold Krille wrote:
> Hi,
> 
> On Friday 07 August 2009 14:54:30 James Stone wrote:
> > In the end, I tracked down my 14 minute xruns to running the SBLive at
> > 44100 instead of 48000.. I wonder if that would help with the OP problem?
> > Now, is this a bug with jack (v 0.116) or just a design problem with the
> > SBLive? I know the SBLive runs at 48000, and has to be resampled (or
> > something similar that I don't understand) to run at 44100, but surely
> > that shouldn't cause xruns.. The slow build of static before the xrun
> > now makes much more sense to me!
> 
> I think this could be the problem also for the OP! Nowadays many sound devices 
> just work with fixed 48000kHz and resample when opened with other rates...
> 

That makes sense to me. The question I have now is: who or what is doing the resampling? Is it the card, internally? Or ALSA? If it's ALSA doing the resampling, then the problem is likely the driver for the card.

Wherever it is, either ALSA driver or the card's firmware or hardware, it may be a 32-bit or 16-bit overflow. When audio cards are running in normal mode, they just sit there most  of the time unless you give them audio. But with JACK running, the card is constantly being fed something (zeroes? I haven't looked to find out what exactly) all the time. You'll notice your interrupt counter going up and up when JACK is running, even if no sound is coming out, for instance.

So my guess is that, every 14 minutes, enough frames are pumped to the card  for that int/long/whatever to overflow. The strange sounds might be as it gets close to that overflow point.

Total wild guess here, but that's where I'd think of looking.

-ken