[SOLVED] jackd as the default sound device

nass · 12-24-2010, 03:04 PM

hello everyone!
I've been fiddling around lately the jack-audio-toolkit. Ideally, I would like to use a jack rack of some effects to improve the audio from an otherwise crappy laptop audio.
I 've installed jack, qjackctl, ardour, audacity and their relevant dependencies.
I also managed to get realtime priviledges to jackd through set_rlimits (and the low latency desktop kernel setting - but no rt kernel) even though at my old laptop this equates to 42ms lag. But that's OK - i'm not planning to capture music on this pc.

The point I'm trying to make here is that applications seem to be racing to use the default sound output device (provided by alsa in my case), so when I am running jackd i have no sound for firefox. Likewise, if jackd is running and i'm running audacious directly with the alsa output plugin , i'll get an (expected) error that snd_pcm_device is busy.

Since the audacious-plugins don't have the jack output plugin included by default, I had to get the sources separately and compile and install them. now I can use audacious through jackd but i'll still have problems with all the other applications (mplayer, xine, firefox etc.).

So is it possible that I can fool all applications into using jackd as their default output device?
alternatively are there jack output plugins for pretty much all applications?

Thank you all for your help
and Merry Christmas!
nass

Ramurd · 12-24-2010, 03:12 PM

Merry Christmas to you too;

If it will be possible to use jack as the default output device, I don't know. However, there are a few pointers I may be able to give.

Given your description, I have the feeling you use KDE3, or some compatability stuff that makes you use artsd. As far as I know it's the only application that will lock your soundcard for it's sole own use, programs that want to produce sound have to go through artsd.

Disabling aRts might already help you on your way; as alsa should be very capable of handling multiple applications producing sound at the same time.

T3slider · 12-24-2010, 07:10 PM

You could install the ugly horrible pulseaudio with the following .asoundrc:

Code:

pcm.!default {
    type pulse
}
ctl.!default {
    type pulse
}

Firefox (and all jack-unaware) apps should output to pulse, which can output to JACK. artsd may work as well. If you're just trying to improve audio, though, there are ALSA plugins that, if they can do what you want, would be a *much* neater and CPU-savvy solution. I would try that first and perma-JACK as a distant second option.

If you must use JACK, though, see here which may or may not help you use Flash and similar without adding artsd/pulseaudio.

nass · 12-25-2010, 08:48 AM

Hello and thank you for your replies.

Ramurd, i'm on KDE4 (slackware-current). so no artsd server. I read that phonon is the sound server of KDE4 but i see no phonon application running, or any such package installed. I setup jackd to use alsa as the output device and as such it must be jackd that's locking alsa completely to itself.

T3slider I looked around for alsa-plugins and their functionality. If I understood correctly, you can set some permanent plugins and corresponding values in ~/.asoundrc file but thats about it. you can't be tweaking knobs real time. So alsa plugins is out of the questions.

It appears what I want is ultimately done by introducing a loopback device (a virtual soundcard) in alsa.
Then you can make the virtual soundcard the default one, and bridge it to your real soundcard through jack. So all applications can continue outputting sound to alsa as before without altering their settings.

I found the relevant howto in alsa unofficial wiki.
http://alsa.opensrc.org/index.php/Ja...to-Jack_bridge

I'll have ago at it and post back the results!

nass · 12-26-2010, 12:57 PM

ok the guide works like a charm. I installed jack-rack and been using a set of effects for all applications that output sound to the default device (that is alsa), unaware that the sound actually reaches the jackd server.

2 things to note:

1) prefer the snapshot version of the alsa-driver (NOT the one in the alsa main page) with the kernel 2.6.36. I read somewhere that up to kernel 2.6.33 the main page version of the driver compiled fine - sorry I didn't keep the link. And I am unsure whats the deal with the intermediate versions of the kernel.
read this thread for info and a download link: http://www.linuxquestions.org/questi...6-36-a-829221/

2) from kernel 2.6.37 the virtual soundcard (loopback) device that is necessary for the above setup will become an option in the mainline kernel, so the separate re-compilation of the alsa-driver will become unecessary!

thats it folks!