[LAU] Regular Xruns?

David Baron d_baron at 012.net.il
Sun Aug 9 07:56:55 EDT 2009

On Sunday 09 August 2009 14:36:26 Paul Davis wrote:
> Ken - again, no picking on your personally, just want to clarify some
> misconceptions for the record ...
> On Fri, Aug 7, 2009 at 10:16 PM, Ken Restivo<ken at restivo.org> wrote:
> > 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.
> no ALSA driver that i am aware of does resampling. however, libasound,
> the ALSA library used by all ALSA applications (including JACK when
> run with the ALSA backend) can resample if you use a device name that
> permits it. the most common device name for this is something like
> "plughw:N", which will do resampling if the underlying hardware does
> not support the sample rate you ask for. it is not particularly high
> quality resampling. if you use the "hw:N" device name, as is
> recommended for JACK, no resampling will ever occur in software.
If I am playing a 44100 file through xmms->jack (set to 48000) to default hw 
out (hw:0 ?)--it sounds 100% OK so something is doing the resampling. The old 

> > 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.
> whenever you start an audio interface, it is running until you stop
> it. perhaps you mean that other programs don't keep the interface open
> when they are not playing audio. that would vary on a case by case
> basis. ALSA also permits the app to leave the card running without the
> app feeding anymore data - the app tells ALSA how to handle the
> requirement to refill the card's data buffer - but i doubt if many
> apps use this part of the ALSA API. in addition,
> > 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.
> nothing is going to overflow for hours. and when it does, nothing
> happens. you're just going to have trust this hand-waving assertion,
> and i'm willing to be proven wrong in the case of a particular
> driver/hw combination.
Since the switch to 48000 does get rid of the regular periodic Xruns (others 
may still occurs--not a rt-patched kernel), if this hypothesis not 
appropriate, what was causing the Xruns (which the fact of their occurance was 
not particularly hardware or kernel dependent though the period may have 

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