[PlanetCCRMA] Pulseaudio and qjackctl

Fernando Lopez-Lezcano nando at ccrma.Stanford.EDU
Thu May 7 09:33:48 PDT 2009

On Wed, 2009-05-06 at 14:58 -0700, Jeff Sandys wrote:
> I am testing Fedora 11, and I got qjackctl to work fine, but I think the
> configuration isn't right.  Here is the part of the note I posted to Fedora
> Forums:  I saw that Fernando weighed in on the Pulseaudio ALSA debate.
> I installed qjackctl on a Live-Preview-XFCE-i686 usb with persistence.
> In the qjackctl connect panel there were no audio output or input ports
> until I installed pulseaudio-module-jack and alsa-plugins-jack per Harald
> Hoyer's Pulseaudio and Jackd tips, (jack-audio-connection-kit was installed
> with qjackctl).
> http://www.harald-hoyer.de/linux/pulseaudio-and-jackd
> I added "liveuser" to pulse-rt and jackuser and noticed that
> /etc/security/limits.conf already had jackuser and pulse-rt added.
> Should pulseaudio-module-jack and/or alsa-plugins-jack be a dependency of
> qjackctl?


While you can use jack over pulse that's not the way I would use it. The
best jack performance (lowest latency) will happen when you connect
directly to the hw: interface of the soundcard with nothing else in
between (and then pulse will not be able to play as jack will be "owner"
of the soundcard).

Do a "cat /proc/asound/cards", that will show which cards are recognized
by the system. Then you can enter the device in the qjackctl "Device"
field as "hw:NAME_OF_CARD" (the name of the card is between [] in the
listing), or "hw:0" for the first card but if you have more than one the
index can change on a reboot).

(Rui: shouldn't qjackctl scan and present the available options?)

> I couldn't get my usb MIDI keyboard working, there were no midi or alsa
> output or input ports in qjackctl connect, and jack complained about not
> finding an ALSA midi seqencer when it started, until i did a modprobe
> snd-seq-oss. What is the default /dev/sequencer?

You don't need the oss compatibility layer. I don't know what may be
missing but oss should not be the answer. 

> Should modprode snd-seq-oss (or equivelent) be part of the standard
> distribution?

Not really. All apps currently support alsa and don't need oss. 

> After that qjackctl ran fine, I didn't have to stop pulseaudio to start jack
> or use any of the other suggestions in Harald's tips. I pounded on zyn for a
> while with jackd -R -r44100 -p250 -n2 with no xruns and about 10% usage.

Because you are using jack on top of pulse, which will add latency that
of course jack will not know about. 

> The XFCE panel volume control lets you select between Pulseaudio and the
> audio card, I had to switch to the card and set the PCM to 100% to get
> sound. This is a nice feature.
> What is the proper was to set up midi with jack so that the midi connectiosn
> show up on the MIDI tab instead of the ALSA tab?  
> Any other pointers to the correct modern linux audio setup is appreciated.

"cat /proc/asound/cards" should show you the cards available, including
the usb keyboard if it has been recognized. What snd kernel modules do
you have loaded?

  /sbin/lsmod|grep ^snd

-- Fernando

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