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2.3. Using the JACK Audio Connection Kit

2.3.1. Installing and Configuring JACK

  1. Use PackageKit or KPackageKit to install the jack-audio-connection-kit and qjackctl packages.
  2. Review and approve the installation, making sure that it completes correctly.
  3. Run QjackCtl from the KMenu or the Applications menu.
  4. To start the JACK server, click Start. To stop the JACK server, click Stop.
  5. Click Messages to see messages, which are usually errors or warnings.
  6. Click Status to see various statistics about the currently-running server.
  7. Click Connections button to see and adjust the connections between applications and audio hardware.

Important

JACK operates with special real-time privileges. You must add all users to the jackuser and pulse-rt groups so they can use JACK. For instructions to add users to groups, see Chapter 22, Users and Groups of the Fedora Deployment Guide, available at http://docs.fedoraproject.org. Do not add users to these groups if they will not use JACK.
With the default configuration of QjackCtl, it chooses the "default" sound card, which actually goes through the ALSA sound server. We can avoid this, and use the ALSA drivers without the sound server, which will help JACK to maintain accurately low latencies. The following procedure configures JACK to connect to the ALSA driver directly.
  1. Open a terminal. In GNOME, choose ApplicationsSystemTerminal. In KDE, click on the application launcher, then choose SystemKonsole.
  2. Execute this command: cat /proc/asound/cards
  3. The cat program outputs a list of sound cards in your computer, which looks similar to this list:
    0 [SB             ]: HDA-Intel - HDA ATI SB
                      HDA ATI SB at 0xf7ff4000 irq 16
    1 [MobilePre      ]: USB-Audio - MobilePre
                      M Audio MobilePre at usb-0000:00:13.0-2
    
    In this example output, the square brackets surround the name of the sound card. The names of the sound cards in this example output are SB and MobilePre.
  4. Identify the name of the sound card that you want to use. If you do not see your sound card in the list outputted by cat, then your computer does not detect it.
  5. Start QjackCtl.
  6. Click Setup to open the "Setup" window.
  7. In the 'Interface' text box, type the name of your preferred sound card with "hw:" in front. With the sound cards listed above, you might write hw:MobilePre.
  8. Save your settings by exiting QjackCtl. If you want to use JACK, restart QjackCtl.