[PlanetCCRMA] Effect on different desktops and desktop effects on latency

Tony White twhite at operamail.com
Tue Sep 17 11:54:34 PDT 2013

Hi Donald,
The short answer to your question is no. The long answer is that to
achieve latencies that are as low as possible, the only limitation is
your hardware. Your sound card in relation to audio work is possibly the
most important piece when using the jack audio server. When you start
the jack audio server you should stop pulseaudio which you can do using
pasuspender -- jackd which will suspend pulseaudio until jack quits ( I
seem to remember that this does not work if you use the dbus interface
for jack.)
The amount of system RAM you have installed will likely reduce the
chances of xruns caused by I/O when the kernel moves data from memory to
a temp file on a physical hard drive or during any other memory
intensive operations. You can configure the kernel to keep very large
amounts of temp data in memory and wait very long times until it flushes
to it disk when it becomes full using /etc/sysctl.d/ or a custom systemd
unit like I do, if you have lots of memory.
Desktop effects are handled by the GPU and as long as you are not using
an Intel on board graphics chip which uses shared system memory I don't
believe it is an issue per se.
As far as the proprietary AMD driver goes; I am able to run jack at 128
frames with 2 buffers with a start delay of 2 seconds and achieve 5.33
msec latency with only the occasional xrun which don't appear to occur
I am using an Intel i5 2500K, Intel desktop board, 20GB of DDR3, an AMD
7950 and I am using the on board audio chip. If your machine is older,
you likely will need to lower the number of frames but it might still be
possible to achieve the golden < 10 msecs latency using jack. But only
if your hardware is good.
You can find out if KDE is providing latencies by lowering the number of
frames but not so much as that you are seeing too many xruns. Run
qjackctl, do some test recording using jack, then stop jackd and logout.
Login using xfce or lxde and try lowering the number of frames and
restart jackd again to see if there is any difference in xruns.
When you do lower the frame number and then restart jack, you will want
to leave it running while you use it to do some more test recordings.
You should not see any xruns or just a single one. If so, you are
hitting the limit of your hardware (qjackctl goes red when an xrun
occurs. You can see the number of xruns in the qjacktl main window. Lots
are bad.)
Hope that helps you to answer your question.

Kind Regards,

  Tony White
  twhite at operamail.com

http://www.fastmail.fm - The professional email service

More information about the PlanetCCRMA mailing list