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User Scripts & Dragons - Realtime/Low Latency Kernel for Audio?

meier - 16.04.2011, 06:49
Post subject: Realtime/Low Latency Kernel for Audio?
Hello everybody,

I hope I'm posting to the right place, and I know that I get to keep the pieces...

That being said, I'm starting to do some music production on my notebook, and I'm wondering whether it would be necessary/advisable to use a non-slh, i.e. realtime/low-latency kernel, for it. Is this even necessary nowadays?

If yes, what would be the least invasive way to go about it? Should I use the pre-compiled kernel with RT-patch applied from http://www.pengutronix.de/software/linux-rt/debian_de.html (as suggested by http://wiki.debian.org/DebianMultimedia)? Or compile my own kernel, as suggested here: http://pkg-freebob.alioth.debian.org/lowlat.html? Are there other/better possibilities?

I'm trying to create some simple backing tracks for guitar practice and ambience "soundtracks" for game modding. I'm using JACK and stuff like QSynth, Hydrogen, Rosegarden, and I'm on a Sony Vaio VGN-FZ11S notebook.

Infobash:

      Code:
running Linux 2.6.38-2.slh.7-aptosid-686 i686 [ sidux 2010-01 Ύπνος - kde-full - (201006131622) ]
CPU Info        2x Intel Core2 Duo T7100 @ clocked at [ 1800.000 MHz ]
Videocard       nVidia G86 [GeForce 8400M GT]  X.Org 1.9.5  [ 1280x800@59.9hz ]
Processes 135 | Uptime 52min | Memory 845.4/2024.8MB


Any hints would be greatly appreciated! Thanks for listening,

Meier
muchan - 16.04.2011, 09:01
Post subject: RE: Realtime/Low Latency Kernel for Audio?
The latest RT kernel is still 2.6.33 version, isn't it?
and I heard (just heard, not tried) that newer version of kernel has already very low latency
that you don't feel the difference...
so.. I'd first suggest try your music setting on current kernel of aptosid, without extra
burden of other processes. (i.e. not starting many deamons and applications in parallel.)

Only when you have latency problem in real, you may consider switching to RT kernel.

makke and holo used to provide RT patched version of slh kernels, but I don't know if they
continue...

On linuxmusicians.com forum, you find some aptosid users there, too.
blackhole - 16.04.2011, 09:13
Post subject: RE: Realtime/Low Latency Kernel for Audio?
Personally I have compliled my own kernel 2.6.33, that is the last version of realtime kernel. A new version was announced for kernel 2.6.37 but now we are at 2.6.38 and nothing is out.
It is true that the last kernels are a lot better for realtime. For example you can use some video player or music player with jack without problems. However, if you need something more a non-realtime kernel is not enough. At 192 khz and 24 bit, for example, and some midi files with linuxsampler and Bosendorfer 290 samples only real time kernel can achieve a useful performance. The same if you are recording multitrack with ardour.

Stay away from pengutronix, since it seems there are some incompatibility with aptosid configuration. If you need an howto for compiling the kernel, let me know.
spock - 16.04.2011, 11:51
Post subject: Re: Realtime/Low Latency Kernel for Audio?
      meier wrote:

I'm starting to do some music production on my notebook, and I'm wondering whether it would be necessary/advisable to use a non-slh, i.e. realtime/low-latency kernel, for it. Is this even necessary nowadays?


I'm no kernel expert at all, but like others say, I don't think it's really necessary any more like it once was. I use Ardour on an RME HDSP 26-channel card (albeit at 48kHz) running slh kernels and experience no xruns with <3ms JACK latency, which is good enough for me. There was a bad phase many months ago when Ardour's GUI would pause for a while (but audio usually continued unaffected), but I suspect Intel graphics issues (or my olde hardware) caused that, and it no longer happens since somewhere in late 2.6.36 or early 2.6.37 vintage.

      meier wrote:

Should I use the pre-compiled kernel with RT-patch applied from http://www.pengutronix.de/software/linux-rt/debian_de.html (as suggested by http://wiki.debian.org/DebianMultimedia)?


Last year I had similar questions, and read this on that very page at Debian Multimedia which confirmed my thoughts:

      Debian Multimedia wrote:

Realtime kernel

The Debian Multimedia team is not working on including a kernel image with the realtime-patches applied in Debian. Much of the realtime-patches have been accepted in the mainline kernel, to the point that for most purposes the stock Debian kernel is suitable even for realtime-like work.

If you'd like to use a kernel with the realtime-patches applied anyway, you might want to consider adding the pengutronix repository


I'd like to take this opportunity to thank slh and all the aptosid devs who make Debian sid so usable.Very Happy I used to use 64Studio but switched when I found sidux, as Linux Audio is one field where you need recent packages.

      meier wrote:

Or compile my own kernel, as suggested here: http://pkg-freebob.alioth.debian.org/lowlat.html?


That page is hindered by no date or hints at age, not to mention even less web design then my Home Page.Laughing It references a thread from the great Dave Phillips from back in 2000, and may not have been changed since 2007:

http://web.archive.org/web/*/http%3A//p ... owlat.html


      meier wrote:

Are there other/better possibilities?


This may help:

http://jackaudio.org/faq

Have fun and funk! Very Happy
slh - 16.04.2011, 14:49
Post subject: RE: Re: Realtime/Low Latency Kernel for Audio?
Kernel 2.6.33 is too old to work with current userspace (mesa/ X.org in particular, but also lirc and many more to come).
blackhole - 16.04.2011, 15:16
Post subject: RE: Re: Realtime/Low Latency Kernel for Audio?
I don't know, but I am writing this inside 2.6.33 kernel realtime now. No errors at boot, no errors at starting kde. Yes, I am using nvidia drivers (that must be patched for realtime). Maybe with nuoveau or some other drivers...

      Quote:

Card nVidia GT216 [GeForce GT 240M] X.Org 1.9.5 Res: 1920x1080@50.0hz GLX Renderer GeForce GT 240M/PCI/SSE2 GLX Version 3.3.0 NVIDIA 256.53

meier - 16.04.2011, 16:27
Post subject: RE: Re: Realtime/Low Latency Kernel for Audio?
I thank you all for your swift and knowledgeable replies. Aptosid features a great community. And what spock said about kudos to slh and all the devs goes for me as well. I had epic fails trying to get Debian Testing to work properly, but never any real problems with Aptosid.

For the moment, I'm trying to find out more about the performance of my setup as is. I'm using Qjackctl's status window for this. Apt-cache search latency came up with a tool called latencytop, but this seems to depend on special kernel configuration parameters, which I would have to do some research on first. Do you people have any other suggestions regarding diagnostics?

If all goes well, I'll increase the difficulty by adding ardour to the mix. And if that leads to a performance disaster, I may take you up on your kind offer, blackhole...

Again, thank you very much,

Meier
horo - 19.04.2011, 16:31
Post subject: RE: Re: Realtime/Low Latency Kernel for Audio?
      Quote:

makke and holo used to provide RT patched version of slh kernels, but I don't know if they
continue...

Yes, I do...
Add
      Code:

deb http://cryptomys.de/experimental/ ./

to your sources.list.d files and do
      Code:

apt-get install horo-keyring
apt-get install linux-kernel-rt-horo


Latest is 2.6.33.9-rt31

Ciao, Martin
muchan - 19.04.2011, 20:49
Post subject: RE: Re: Realtime/Low Latency Kernel for Audio?
Martin, sorry for my "Japanese spelling". (hard to distinguish r and l in my mind...)
meier - 22.04.2011, 09:45
Post subject: RE: Re: Realtime/Low Latency Kernel for Audio?
Thanks, Horo,

will try it as soon as I can,

meier
Maxei - 16.05.2011, 09:07
Post subject: RE: Re: Realtime/Low Latency Kernel to test pianoteq
Hello,
Can someone please point me in the right direction as to get and install a realtime kernel. I need to run an application called Pianoteq, which is connected to the electronic keyboard through JACK and ALSA. I'm using ubuntu studio 11.04 and have horrible latency and crackling. Your help is appreciated.
muchan - 16.05.2011, 10:12
Post subject: RE: Re: Realtime/Low Latency Kernel to test pianoteq
Wait just a little that soon next .39 kernel will be released.
I've heard that from 39 on, it is actually RT kernel.
(the patches for RT kernel, or their equivalent has been included in mainline?)

and... please correct me if I am wrong.
horo - 06.11.2011, 11:53
Post subject: linux-3.0.7-rt20
Hi,

new version 3.0.7-rt20 available at
      Code:
deb http://cryptomys.de/experimental/ ./


Built from vanilla kernel 3.0.7 + rt20 patch + make oldconfig from 3.0-7.slh.2-aptosid-686

Procedure see above ^^

Ciao, Martin
plutek - 24.08.2012, 01:57
Post subject: RE: linux-3.0.7-rt20
when i follow your procedure, during apt-get update i get this error message:
      Code:

GPG error: http://cryptomys.de ./ Release: The following singatures couldn't be verified because the public key is not available: NO_PUBKEY A8ED5E79417481A3


then, when i try to do apt-get install horo-keyring, i get this one:
      Code:

Unable to locate package horo-keyring


viewing the directory listing in a browser, i see a 3.0.9-rt25 in cryptomys.de/experimental/binary which i'm interested in testing!

please let me know if i need a different procedure for this.

cheers!
.pltk.
hubi - 25.08.2012, 08:26
Post subject: RE: linux-3.0.7-rt20
I don't think horo's repo is still working. Delete the source from your apt sources list and update the apt database.

hubi
horo - 27.08.2012, 08:07
Post subject:
Hi plutek,

just checked the repo (from my win laptop in the office), horo-keyring is available:
http://cryptomys.de/experimental/binary/
Will check this evening from my debian system.
Hubi, you're pretty right, I didn't create new versions since last year because the 3.x kernels are good enough for my audio requirements.

Ciao, Martin
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