[ubuntu-studio-users] Real-time - Was: ubuntu-studio-users Digest, Vol 79, Issue 27

[Mike Holstein]

On Nov 28, 2013 3:09 AM, "Ralf Mardorf" <ralf.mardorf at alice-dsl.net> wrote:
>
>
>
> On Wed, 2013-11-27 at 19:53 -0500, Mike Holstein wrote:
> > On Wed, Nov 27, 2013 at 2:57 PM, Alex Armani
> > <alex.armani at rocketmail.com> wrote:
> >         What are the advantages and disadantages of using the low
> >         latency kernel? How is this different from the real time
> >         kernel? I use the Gnome 3.8 desquetop 64 bit studio.
> >
> > the realtime kernel is basically discontinued. you can add it via ppa,
> > or build it yourself. if you need the realtime kernel, you'll know,
> > and seek it out. what are its advantages? lowlatency. disadvantages?
> > the things that are compromised to provide lowlatency and audio
> > priority can (and will) change performance of other things, such as
> > power management. to address these differences between a normal, well
> > supported, standard generic kernel, and the realtime kernel, a
> > compromise was introduced. the lowlatency kernel is supposed to
> > address these concerns, and provide an appropriate kernel that can do
> > realtime at lower latency settings without the compromise in
> > performance in other areas. if you are considering a realtime kernel
> > via PPA, keep in mind those sources are not officially supported.
> > there is no reason to remove any kernels. you can always keep the
> > lowlatency and the generic, as well as a realtime kernel from a ppa
> > installed, and choose between them at boot time from the grub menu.
> > its likely you dont need lowlatency at all. if you are doing realtime
> > effects or software synths as an instrument, you will want lower
> > latency, but really anything around or under 8ms is plenty. enjoy!
>
> There are different levels of real-time for Linux and non of the levels
> does provide hard real-time, but nowadays it's that close to good old
> hard real-time, that it doesn't matter.
>
> Latency shouldn't be an issue, nowadays many amateur engineers expect
> lower latencies for virtual stuff, then real musical instruments do
> provide. Important is, that there is no jitter.
>
> If you do MIDI work with external MIDI gear, than the lowlatency kernel
> is not a very good choice. To get rid of MIDI jitter, you need the
> hardest real-time the rt-patch does provide and very good hardware.
>
> Preemption Model
>   1. No Forced Preemption (Server) (PREEMPT_NONE)
>   2. Voluntary Kernel Preemption (Desktop) (PREEMPT_VOLUNTARY)
>   3. Preemptible Kernel (Low-Latency Desktop) (PREEMPT__LL)
>   4. Preemptible Kernel (Basic RT) (PREEMPT_RTB)
>   5. Fully Preemptible Kernel (RT) (PREEMPT_RT_FULL)
>
> Regards,
> Ralf
>
> PS:
>
> Real-time at the moment IMO is a serious issue
>

It's a non-issue. There are 2 types of kernels in the default repos. The
lowlatency one is the most appropriate for lowlatency needs. If a different
one is determined more appropriate, one is welcome to seek out one from
unsupported sources. Cheers!

>
http://lists.linuxaudio.org/pipermail/linux-audio-user/2013-November/095098.html
> https://lists.ubuntu.com/archives/kubuntu-users/2013-November/058744.html
>
> This one has got follow ups:
> http://archaudio.org/pipermail/archaudio-discuss/2013-November/000307.html
>
>
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