[LAU] Kmix + jackd strange behaviour

[Edgar Aichinger]

Am Donnerstag 30 Oktober 2008 schrieb Crypto:
> On Thursday 30 October 2008 11:04:38 Rui Nuno Capela wrote:
> 
> > this device list, assuming you're referring to the qjackctl setup
> > drop-down menu as shown by the [>] button on the right to interface and
> > input/output device entry fields and "alsa" is the selected driver, is
> > just the enumeration of all alsa_pcm devices available in your system.
> >
> > this list is not created by qjackctl. it is indeed queried by qjackctl
> > to the alsa control layer and is built everytime you pop the menu up, so
> > it doesn't matter at all whether you restart qjackctl or not.
> >
> > otoh, i suspect that it is amarok, which you must ensure that its xine
> > engine is sure having jack as its output plugin, that needs to be reset
> > or recycled whenever you restart jackd (via qjackctl).
> >
> > byee
> 
> Ah, I have found it. It is a matter of confusion ;-) And, unfortunately, it IS 
> a problem in qjackctl. Maybe it is a feature though ;-)
> 
> I have had a look at the .jackdrc file which in my case contains a single 
> line:
> 
> /usr/bin/jackd -R -dalsa -dhw:1 -r48000 -p128 -n2 -Phw:0,0 -S -o2 -Xseq
> 
> This is the line that jackd gets on startup when launched by qjackctl.
> 
> It is set to -d hw:1 which means output to hw:1 (my external USB device).
> 
> The tricky thing is the -P parameter. 
> 
> It means: -P --playback Provide playback ports. Optionally set device 
> (default: none)
> 
> It is wrongly set to hw0:0 which is the onboard sound of my notebook.
> 
> Why is that?
> 
> Look in qjackctl: one can select from the "Audio" menu to have duplex 
> or "Playback only" or "Capture only".
> 
> If You - as I did - select "Playback only", then the menus for "Input Device" 
> and "Output Device" are greyed out and cannot be selected. I thought that the 
> ONLY relevant device, that is, the device for audio output in this case, is 
> then selected ONLY by the menu "Interface".
> 
> Unfortunately, the values of the menu "Output device" is still saved in 
> the .jackdrc file and therefore sent to jackd.
> 
> So: if the "Output Device" is greyed out and/or one has not been set before to 
> the correct output port (in my case: external USB card), then the wrong 
> output device will be placed in the .jackrc file and sent to jackd.
> 
> It is easy to circumvent this, though: 
> 
> -> Select "duplex" in the top menu,
> -> Set both "Output device" and "Input device" (just in case) to the desired 
> ports, in my case that is external USB audio device,
> -> revert top menu to "Playback only" and select external USB device (again) 
> in the "Interface" menu
> -> start jackd, which will save new .jackdrc file which now looks like this:
> 
> /usr/bin/jackd -R -dalsa -dhw:1,0 -r48000 -p128 -n2 -Phw:1,0 -S -o2 -Xseq
> 
> It contains the -P option which now outputs to hw:1,0 which is external USB 
> audio correctly.
> 
> Suggestion for improvement: Leave out the "Interface" menu on top and switch 
> interfaces only by "Input Device" and "Output Device". Grey out (make 
> unselectable) the Device which is not relevant, i.e. if chosing "Capture 
> Only" grey out "Output Device", but make sure that the output device is not 
> placed in the jackdrc file. And vice versa.
> 
> It seems to me like the three interface menus are treated differently. Maybe 
> there was a good reason to include the -P option in the jackdrc-file?

Well and what if you set "Interface" to your hw:x,x device, "Input device" and 
"Output device" to "default"? Here this results in a ~/.jackdrc file containing 
-P only, omitting device name, which should also work for you...

AFAIK the In/Output device choice is not a very old feature in jack, and its 
intention is to let you choose different devices for each, in cases where that's 
possible (I don't know a real-world use case, and may be missing the picture). 
If you don't want to do that you should leave those two options alone ("default" 
setting in qjackctl)

> 
> Regards,
> Crypto.
> 
> 
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> 

Edgar