realtime kernel for audio recording

empthollow · 2010-05-15 01:17:23

I have an old laptop I'm trying to record music with. I tried using the standard arch kernel with minimal daemons and a lightweight desktop. I still get glitching/ skips in my recordings and lots in playback. As i understand it, a realtime kernel is the solution to this. I know AUR has a realtime kernel, but after reading the 'realtime for users' archwiki article i'm not sure what I need to do to actual cause the audio processes be given a higher priority. I'm using ardour with jack and lsdpa plugins. If anyone has ideas or insights i would appreciate them! Thanks

Last edited by empthollow (2010-05-17 06:29:42)

ngoonee · 2010-05-15 04:40:35

Have you actually tried installing one of the real-time kernels? You just need to modify your limits.conf after that.

The point of real-time is not that audio processes are given a higher priority (though they are) but simply that RT processes (JACK in particular) are guarunteed to be proceessed in some small amount of time.

empthollow · 2010-05-15 05:21:30

I did install one, but couldn't tell what it was doing and didn't know enough about it to know if I had it set correctly. Durring an upgrade it somehow got uninstalled and a normal kernel was installed. I figured I'd see if it work and, well, it didn't. Thanks for clearing that up, I'll try installing a realtime kernel again and editing limits.conf.

Allan · 2010-05-15 05:34:52

Try the arch-audio supplied rt kernel: http://repos.archaudio.org/stable/i686/

ngoonee · 2010-05-15 06:13:46

empthollow wrote:

I did install one, but couldn't tell what it was doing and didn't know enough about it to know if I had it set correctly. Durring an upgrade it somehow got uninstalled and a normal kernel was installed. I figured I'd see if it work and, well, it didn't. Thanks for clearing that up, I'll try installing a realtime kernel again and editing limits.conf.

You can check whether its installed by searching your local pacman-monitored packages. If its installed it won't get uninstalled (barring dependency problems which are uncommon with kernels). Did you edit your menu.lst (assuming you use GRUB) to boot the RT kernel?

As Allan said, archaudio provides an RT kernel. But if you don't know what I was talking about in the previous line you'd still need to find out, they don't do automatic GRUB editing for you I think.

EDIT: nor should they....

Last edited by ngoonee (2010-05-15 06:13:58)

archman-cro · 2010-05-15 07:32:58

You probably don't need rt. Just fiddle around with JACK settings, they are very important, and look for the limits.conf ngoonee said about. I'm recording music with ~5ms latency with a "normal" kernel with Reaper through wine.

arch0r · 2010-05-15 08:28:11

@ archman-cro: are you using other software besides reaper for audio recording under linux?

the archaudio project is really nice, just grab qjackctl, jack2, wineasio and wine, import the wineasio.ddl and execute reaper :>

the only thing which annoys me is that i have always to link and route the sound devices to each other via qjackctl. there's no really plug and play under linux when it comes to sound recording

archman-cro · 2010-05-15 11:18:31

@arch0r, I don't use anything except Reaper really, cause Ardour annoyed me a few times, LMMS doesn't look good to me, and the rest is a pain. I rather go with powering on jack with qjackctl thru wineasio and wine and launch Reaper. I tried going with Rosegarden by routing some dll drum machine from jack to rosegarden, but that's just a pain in the ass. Power on Reaper only and that is enough and the best for me.

Dieter@be · 2010-05-15 16:01:44

archman-cro wrote:

You probably don't need rt. Just fiddle around with JACK settings, they are very important, and look for the limits.conf ngoonee said about. I'm recording music with ~5ms latency with a "normal" kernel with Reaper through wine.

yes, this often mostly works. until you have an app or irq that causes some load and gives you massive xruns

empthollow · 2010-05-17 00:11:35

I've compiled 2.6.33.3 with rt patch. The kernel works but my wireless card needs madwifi drivers and I can compile them fine against the kernel, but when I load the modules ifconfig will show the device and for about a minute I get scan results. Then all the networks dissapear. So, given the time I've spent compiling over the last day or so... and night, I am interested in the archaudio pre-compiled kernel - thanks for the link. For now I'm going to stick with ardour because I am familiar with the interface...plugins...etc. As far as the jack settings go, where do I change them and which ones helped you the most. Thanks for all the input.

EDIT.UPDATE:
I installed qjackctl, it looks like all the settings I could want but I don't know what to change.

Last edited by empthollow (2010-05-17 05:41:15)

archman-cro · 2010-05-17 12:38:13

What to change? Change what you need. I get a nice latency with these settings: Frames/Period 128, Periods/Buffers 3, H/W Monitor and Soft Mode ticked. Try it on a "default" kernel if you want.

Arch Linux

#1 2010-05-15 01:17:23

realtime kernel for audio recording

#2 2010-05-15 04:40:35

Re: realtime kernel for audio recording

#3 2010-05-15 05:21:30

Re: realtime kernel for audio recording

#4 2010-05-15 05:34:52

Re: realtime kernel for audio recording

#5 2010-05-15 06:13:46

Re: realtime kernel for audio recording

#6 2010-05-15 07:32:58

Re: realtime kernel for audio recording

#7 2010-05-15 08:28:11

Re: realtime kernel for audio recording

#8 2010-05-15 11:18:31

Re: realtime kernel for audio recording

#9 2010-05-15 16:01:44

Re: realtime kernel for audio recording

#10 2010-05-17 00:11:35

Re: realtime kernel for audio recording

#11 2010-05-17 12:38:13

Re: realtime kernel for audio recording

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