Arch Linux

kungfoo

Member

Registered: 2006-09-09

Posts: 43

Ardour + Jack + real low latency

So I got this working almost perfectly. I just want to make sure, I get what i bargained for:

What are the best settings for audio recording with the current kernels? I have realtime capabilities for the audio group, that works nicely.
Things that matter to me:
- which services to turn off for recording?
- SMP on or off? (On a Pentium4, with "emulated" 2 processors)
- Kernel Preemption?

I have a M-Audio Delta1010 here and I can get as low as 5ms of latency (as repoted by ardour) without constant xruns. Still I think Ishould be able to even get it lower....
Any advice??

kungfoo

Member

Registered: 2006-09-09

Posts: 43

Re: Ardour + Jack + real low latency

Anyone?? Most advice on the net I found was on the old kernels, which I don't want...

jochen

Member

From: Germany

Registered: 2004-06-01

Posts: 102

Re: Ardour + Jack + real low latency

Hi,

you can have decent realtime performance with an unpatched recent kernel, or apply the "molnar-patch"  http://people.redhat.com/mingo/realtime-preempt/ and get even better.

Have a look at:

http://lac.zkm.de/2006/papers/lac2006_lee_revell.pdf
http://tapas.affenbande.org/

I'm using kernel26suspend2 which has a better config than kernel26 in terms of:

CONFIG_HZ_1000=y
CONFIG_HZ=1000

further on I use ext3 as filesystem and have the following line in rc.local:

echo 64 > /sys/block/hd*/queue/max_sectors_kb

I hope this helps,
regards
jochen

kungfoo

Member

Registered: 2006-09-09

Posts: 43

Re: Ardour + Jack + real low latency

Thanks! I'm trying to get the kernel patches applied and a kernel baked. Will report how well that worked out!!

It would be ridiculously cool to have my Delta1010 run with buffer sizes of 2x32 and 48khz, resulting in a latency of about 1.3ms.

That's would definetely beat the sh*t out of ASIO

kungfoo

Member

Registered: 2006-09-09

Posts: 43

Re: Ardour + Jack + real low latency

Didn't quite work out. The kernel panicked on bootup. Gotta do some work right now. Did you ever try to build the kernel with the molnar-patch with a config that will keep it working "the arch" way?

I came from gentoo and really liked the simplicity of arch... Compiling yet again

test1000

Member

Registered: 2005-04-03

Posts: 834

Re: Ardour + Jack + real low latency

i'm not sure i understand you, ("[...] arch way"), but the easiest would probably be to make your own repo and put it in pacman.conf infront of the other mirrors and have your custom kernel inside there, and make a new package to put in there when you feel your too lagging behind the official arch kernel. Ofc you could always just IgnorePkg kernel26 (pacman.conf again...) but that might throw you for a loop when something depends upon a new kernel.

(presumably it should happen sometime in the future )

meaning go to /var/abs (just saying incase you don't know, I don't want to make presumptions here) and find the kernel and add the patches then make a repo and put the .pkg in there ++

---

KISS = "It can scarcely be denied that the supreme goal of all theory is to make the irreducible basic elements as simple and as few as possible without having to surrender the adequate representation of a single datum of experience." - Albert Einstein

kungfoo

Member

Registered: 2006-09-09

Posts: 43

Re: Ardour + Jack + real low latency

No I didn't mean the kernel not getting over-written by updates. I still like a kernel for everyday work like surfing the net and such. The one fpr audio work would have to be selected on boot up. But first I'd need one that does not give me a kernel panic before even mounting the root file system...

edit:
Right now I'm trying the mm kernel...

kungfoo

Member

Registered: 2006-09-09

Posts: 43

Re: Ardour + Jack + real low latency

I'm still new to the whole pacman package system and how to pack up stuff. But if someone made a package of a 2.6.18 kernel or s, with the Molnar patch applied, one could really use that as an argument for arch, targetting audio users.

If anyone does know how to do this, I'd be sooooooo thankful...

jochen

Member

From: Germany

Registered: 2004-06-01

Posts: 102

Re: Ardour + Jack + real low latency

Do you really need that low latency? You should be able to get 5ms without xruns with a unpatched 2.6.18 kernel. For me that's enough.

Btw. the realtime patches are going to be integrated in the kernel: http://www.internetnews.com/dev-news/ar … hp/3627831

kungfoo

Member

Registered: 2006-09-09

Posts: 43

Re: Ardour + Jack + real low latency

If the realtime patches would make it to the kernel: awesome.
This is supposed to be used on a prosumer recording PC so, yes latencies that low, without any xruns would be good. Right now I'm running at 2.6ms and get the occasional xrun.

kungfoo

Member

Registered: 2006-09-09

Posts: 43

Re: Ardour + Jack + real low latency

Ok tried and tried again on the laptop and I got my shitty laptop sound card down to 1.2ms of latency, with no xruns except for huge audio connection changes (you usually don't do that when audio is running anyway). Will try again at home and report back!!

Edit: Report:
-------------------------------------

So I tried this on my desktop for two hours straight. Used a Stock 2.6.19-rc6 kernel and tried to apply the patch. Patch ran fine, but the kernel build always failed somewhere, some functions were missing to the linker.
Went down to 2.6.18, downloaded Ingos patch, recompiled and ZIFF. there you go.
Jack runs nicely with a framesize of 32, but generate quite a bit of context switching overhead. This gets me a latency of 0.7ms in Ardour and NO xruns whatsoever. (At 48khz).
Right now I'm running at 64 frames/period, with 32 jack alone uses up 10% of CPU power, just to run....

64 frames/period, gives me a latency of 1.4ms at 48khz. AWESOME. If anyone else needs help with this, or is interested in whatever other variables there are in the system, feel free to ask, I'd be happy to help!!

broch

Banned

From: L.A. California

Registered: 2006-11-13

Posts: 975

Re: Ardour + Jack + real low latency

rt kernel will slow down/make desktop quite jerky. rt is really bad for overall performance.
so if this is dedicated box get 2.6.19-rc5 (not 2.6.19-rc6 as you did) and patch it.
best multimedia fs is xfs (ext3 drops frames during video editing for example). This was proven few times in different tests.

rt patch in 2.6.18/19 is devised for embedded devices and has not much to do with desktops.

if this is more amateurish multimedia editing and box should serve as desktop too, then forget about rt patches. tune file system, re-compile kernel, kill unused services. Get as much RAM as you can