Tutorial: Realtime (RT) Audio on Linux: The Basics (for Laymen)

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This video provides a simplified explanation of what RT audio is, what its purpose is, and how to set it up on newer (2.6.xx) linux kernels.

Please note that the explanations in this video are gross oversimplifications and are intended for the technically savvy, but not for linux experts!

The information currently floating around both youtube and the web in general is generally VERY outdated and far, far more complicated to use than it should be. Realtime audio is a snap to set up and…

22 Comments

  1. Dude, these are really superior tutorials. Why'd you stop making them? I'm curious, followed your link from a comment on Reaper portable (KVR forums.) Do you use Reaper in Linux? I like the idea, but found any user-error led to "could not start Jack!" Love Ubuntu, but ease of use keeps me on the Windows partition most days.

  2. Contrary to a lot of misinformation on the web, there is no reason to include a line here that provides enhanced "niceness" control, which is completely irrelevant for realtime scheduling and low latency audio applications.

  3. So what would be the point of having a real time kernel? Isn't it tweaked to help get the configuration of limit.conf get an even lower latency with the hardware?

  4. I'm afraid all it does is just allows a non-root user to renice processes. In order to get hard real-time perfomance one needs to run patched kernel. I tried doing things adviced in this video but got no perfomance increase (comared to same thing ran with root). After patching a kernel I can run JACK with under 1ms latency with no Xrun's. Cheers

  5. @jaaxxone This is untrue. First off, placing users within in Audio group doesn't have anything to do with determining what programs use RT priorities; it's simply a naming system used to keep things straight if a lot of users use your system. Programs don't know (or care) what user group you're a member of. Secondly, programs don't inherently use unbounded amounts of system resources; they have to specifically be configured to do so.

  6. Not sure about setting your limits at the user level. Would be better to use the @audio group so only those processes get the increased privs. Otherwise, any old user process (gnome panel, notifications, browsers, etc) can steal resources during the middle of your recording sessions!

  7. @Ejacka Try actually logging in as root rather than using sudo. If that doesn't work, you may want to alter your chmod tactic… Using chmod ugo=rwx (or some variation thereof) has always been more reliable and straightforward for me. (Also, doesn't a hyphen before the permissions arguments remove from a file/directory?)

  8. Changed file permissions:

    sudo chmod limits.conf -rwxrwxrwx

    but got this message:

    "Could not save the file /etc/security/limits.conf.

    You are trying to save the file on a read-only disk. Please check that you typed the location correctly and try again."

  9. @fatsterfatster A soft limit is a default value when a user logs in, and this value can be increased using the terminal "ulimit" command. However, we're not interested in either a soft limit or a hard maximum limit, nor using "ulimit" to manually change anything, so we don't have to bother with hard or soft at all.

  10. @pooh1234567890 Programs that can make use of realtime priority must have a software switch specifically stating to use RT. For example, JACK has an option stating "Realtime priority." Most programs do not contain this option.

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