[LAU] midi keyboards, jackd, low latency

torbenh at gmx.de torbenh at gmx.de
Thu Feb 26 21:36:55 EST 2009

On Thu, Feb 26, 2009 at 06:21:48PM -0500, Paul Davis wrote:
> On Thu, Feb 26, 2009 at 4:20 PM, tizo <tizone at gmail.com> wrote:
> > Hi there,
> >
> > Sorry about my previous mail. I was just starting to write a draft
> > about the topics I want to ask, and I accidentally push the send
> > button.
> >
> > Well, my goal is to play two midi keyboards, sending the events
> > through jackd, to qsynth. My computer is a Laptop HP 550, with HDA
> > Intel sound card, 3 GB of memory, and a Core 2 DUO CPU of 1.40 GHz. My
> > OS is UbuntuStudio 8.04, with kernel 2.6.24-23-rt.
> >
> > First of all, I cannot run jackd without xruns, if I configure it with
> > 32 frames per period, or less. I am running it as root, with realtime,
> > and a priority of 70. As soon as I run it, it starts to count xruns,
> > and I am only executing jackd.
> 32 frames per interrupt is VERY ambitious with an Intel HDA chipset. Its not
> impossible but every single part of your system has to be "just right" for
> this to work. I would start with a less ambitious goal first, and get some
> experience with the setup before trying to get all the way to this latency
> level.
> moving to USB will likely make things worse. latencies like this are best
> accomplished with good, prosumer level PCI audio interfaces.

and most certainly not with a kernel that old.
the old hda drivers are totally broken. 

a quick test on vanilla 2.6.28 shows it runs at -p32 -n3.
but it gives me some xruns when i switch desktop.
-n2 is not possible. i get xrun streams.

torben Hohn
http://galan.sourceforge.net -- The graphical Audio language

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