[LAU] Re: Pops and clicks but no xruns

Paul Davis paul at linuxaudiosystems.com
Sun Apr 8 18:35:16 EDT 2007

On Sun, 2007-04-08 at 23:39 +0200, Karl Hammar wrote:
> James Stone <jamesmstone at gmail.com>:
> > On Sun, Apr 08, 2007 at 01:38:34PM +0200, Karl Hammar wrote:
> > > Andrew Burgess <aab at cichlid.com>:
> > > > Paul Davis wrote:
> > > > >> What could cause clicks without xruns? I'm baffled.
> > > > >PCI bus hogging, for one thing. consider running a script like this
> > > ...
> > > >     setpci -s $p latency_timer=ff
> ...
> > I am slightly confused. Is it necessary to increase the latency
> > timer for a pci sound card? This seems slightly
> > counter-intuitive. Wouldn't this reduce the performance of the
> > sound system through that card?
> Performance and latency is different things. In audio we accept all 
> latencies below 30ms (I think), less than that does not gain anything.
> But we can gain bandwith by using longer bursts, thus a higher latency 
> (within bounds) gives us greater performance.

no, this is not really accurate.

the PCI latency timer determines how long a device may own the PCI bus
for, it has nothing to do with audio latency. therefore, if your system
allowed the video interface to hog the PCI bus for a relatively long
time, but limited the audio interface to only short periods of bus
ownership, then audio performance will suffer.

the script i posted first resets *all* devices to an acceptable
middle-of-the-road timer setting, then specifically allows the audio
interfaces to own the bus for even longer.

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