The JACK audio connection kit is a power tool for serious audio users. It is a low-latency sound daemon that acts like a switchboard for all the sound streams in your computer. It is not a replacement for ALSA and other sound subsystems--it manages the streams coming in and out of your sound devices. recordMyDesktop supports JACK, so you can use it to configure your audio capture sources. Suppose you want to capture your sound card output, like we did last week with ALSA. Install JACK and its graphical control panel, qjackctl. This should appear in your multimedia menu as JACK Control. Fire it up and click the Connect button. You should see something like Figure 1. Click on Capture 1 and Playback 1, then the Connect button. Do the same for Capture 2 and Playback 2.

Now go to the Sound tab in recordMyDesktop, and make it look like Figure 2, with both of JACK'S capture devices selected. Start recordMyDesktop, and then open the Connect menu in JACK. You should see the new connections as in Figure 3.

If you can't record sound from your soundcard, you have a lot of company--it doesn't always work. I haven't figured out if it is some kind of kernel problem, a recordMyDesktop bug, a problem with low-end onboard sound, or what. I have found that recording from a microphone works every time.

JACK is probably overkill if you have only a single sound card. But when you have multiple sound devices it's a fast way to switch between them. Suppose you have a USB microphone, and you want to narrate your screencast. Go to the Setup menu in JACK and select your microphone as the recording source, as in Figure 4, and then select the JACK capture devices in recordMyDesktop. All done, and it doesn't change the sound settings for your computer.

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