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New feature request - multiple sound cards with QJackCtl

Hello Rui

If you would like to make yourself even more popular with Linux audio users then a solution for this feature in QJackCtl would be your ticket...

On the right hand side of the set-up dialog the user can select which sound-card (hw:0, hw:0,0, hw1: etc..). Only one sound card can be selected - that is a limitation of jack 1 (I guess jack2 is the same). To use 2 or more sound-cards simultaneously it is necessary to create a virtual sound-card (in super-user mode) by modifying many configuration files in the /etc directory. This is rarely successful when attempted by the normal user.

The code in ALSA for joining inputs and outputs from multiple sound cards was written by Takashi Iwai and as far as I know has been working since 2002 or so... What is missing is a configuration tool with GUI for the average user (like me).

Then again as a normal user I would expect the choice to select more than one sound to be in the right hand side of QJacjCtl's set-up window...

How about it?


rncbc's picture

I'm afraid that feature might not be a good idea. That is, it would be greatest if it worked for jackd, in general.

You know, that jack was designed to work against only one sound-card device and its ALSA backend driver is coded explicitly with that rule in mind, so to speak. You can of course make it work with combined virtual devices given that you can get it all correct magic on the asoundrc configuration file.

It's all highly tricky, unreliable and prone to too many disparate problems that depends on each particular device setup and configuration. Not speaking that you'll have to tune for high-latencies, something that JACK is not well suited or overkill :) Not easy, not even for the expert ALSA technician which I am not ;)


Perhaps then a version of Jack with serious audio in mind, or even professional audio? Many audio people would use a number of cards/devices to get the number of channels they want, and very few cards provide for even 36 input channels in a single card. The comment about sampling sync drift is quite bizarre, but I read it often in the set up for Jack etc, even though practically all good cards/devices are provided with Word sync or other methods of locking the sync. I have spend hours trying to decipher the magic of .asoundrc and getting Qjackctl to use the virtual soundcard. It can probably be done with command line, but really as soon as I read command line I think maybe they want me to put the code on a floppy disk while wearing flares too (command line should always be available but never needed). I have a RME9652 card and a FCA1616 USB (both pretty standard for low end or live mixing) and I can get them to both appear in Ardour under Windows 7 ... but can't under UbuntuStudio , even though I have followed all the tutorials and the info in the ALSA manual. You should need to invoke magic and write config files to perform a standard sort of configuration (eg RME + FCA1616/ADA8200). I understand there is a problem with the control of a number of different cards, as the routing would need to know to which card you wanted to change a parameter of, and obviously the sampling protocols have to match.

What about having support in qjackctl for alsa in/out and for doing the sorts of setups described
at the alsa wiki

for people with firewire cards to be able to use them as general purpose soundcards in linux.

Also it'd be nice if qjackctl used the device name instead of hw:1 so when cards are plugged in in different orders then the config persists as decribed at the fedora musicians guide to using jack

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