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#1 2006-03-14 01:27:12

Registered: 2006-02-20
Posts: 29

Problems with Jack audio and realtime


I'm trying to configure jack-audio-connection-kit to work in realtime as a normal user. I have followed the "Realtime for Users" entry in the wiki and edited /etc/security/limits.conf as:

@audio          -       rtprio          70
@audio          -       nice            -10
@audio          -       memlock         250000

but the jack server doesn't work very well. I get a lot ot xruns (about 5 per minute) even when I'm not using any audio. This is the output of qjackctl:

02:13:25.922 Patchbay deactivated.
02:13:26.176 Statistics reset.
02:13:26.395 MIDI connection graph change.
02:13:29.184 Startup script...
02:13:29.184 artsshell -q terminate
can't create mcop directory
Creating link /home/johannes/.kde/socket-archer.
02:13:29.556 Startup script terminated with exit status=256.
02:13:29.556 JACK is starting...
02:13:29.557 /usr/bin/jackd -R -dalsa -dhw:0 -r48000 -p1024 -n2
02:13:29.562 JACK was started with PID=3886 (0xf2e).
jackd 0.100.7
Copyright 2001-2005 Paul Davis and others.
This is free software, and you are welcome to redistribute it
under certain conditions; see the file COPYING for details
JACK compiled with System V SHM support.
loading driver ..
apparent rate = 48000
creating alsa driver ... hw:0|hw:0|1024|2|48000|0|0|nomon|swmeter|-|32bit
control device hw:0
configuring for 48000Hz, period = 1024 frames, buffer = 2 periods
Note: audio device hw:0 doesn't support a 32bit sample format so JACK will try a 24bit format instead
Note: audio device hw:0 doesn't support a 24bit sample format so JACK will try a 16bit format instead
nperiods = 2 for capture
nperiods = 2 for playback
02:13:31.605 Server configuration saved to "/home/johannes/.jackdrc".
02:13:31.607 Statistics reset.
02:13:31.634 Client activated.
02:13:31.638 Audio connection change.
02:13:31.653 Audio connection graph change.
02:14:47.445 XRUN callback (1).
**** alsa_pcm: xrun of at least 395.915 msecs
02:14:58.447 XRUN callback (2).
**** alsa_pcm: xrun of at least 399.379 msecs
02:15:32.443 XRUN callback (3).
**** alsa_pcm: xrun of at least 395.860 msecs

Those things make the sound choppy.
I also have very bad latency, 42,7 msec...
I'm using the standard arch kernel:

Linux archer 2.6.15-ARCH #1 SMP PREEMPT Sun Feb 12 18:36:42 CET 2006 i686 Intel(R) Pentium(R) M processor 2.00GHz GenuineIntel GNU/Linux

I used Ubuntu before I switched to Arch, and there jack in realtime worked fine, so it's not because of the hardware. Back then I had to add a kernel module named "realtime-lsm", but according to the wiki that is not needed in Arch. Is there a solution for this problem?


#2 2006-03-14 01:31:26

Schwag Merchant
From: Medicine Hat, Alberta, Canada
Registered: 2004-01-18
Posts: 5,986

Re: Problems with Jack audio and realtime

What's your video card and alsa configuration? I had a similar problem with my via onboard chip and had to change a setting "Surround Jack Mode" from "Shared" to "independent".  So I'd say play with alsa. Maybe you can copy your alsactl from the ubuntu system?



#3 2006-03-14 15:41:29

Registered: 2006-02-20
Posts: 29

Re: Problems with Jack audio and realtime

lspci gives me:

00:1f.5 Multimedia audio controller: Intel Corporation 82801DB/DBL/DBM (ICH4/ICH4-L/ICH4-M) AC'97 Audio Controller (rev 03)

I don't seem to have a "Surround Jack Mode" setting in alsamixer.

I have tried playing around with alsa, but I can't seem to get it right... And I have no idea if that is the problem. I will try using the alsactl from ubuntu.

It seems that if I change the Frames/Preiod and Sample Rate settings in qjackctl I can get more or less xruns, but they never go away fully. If I uncheck the realtime option in qjackctl I get lots of xruns.

I read somewhere that you need to have realtime-preemption in your kernel. The option name is CONFIG_PREEMPT_RT. I checked /boot/kconfig26 and it seems that option is not present in this kernel. Normal CONFIG_PREEMPT is set to "y" though. Might this be a problem?


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