Ubuntu cleverness Part 5. realtime-lsm February 20, 2006
Posted by oktyabr in audio, debian, linux, realtime, ubuntu.trackback
“realtime”, in the linux audio world, is required for professional level recording and processing. It allows a normal user to access audio apps in a kernel state that provides much lower audio latencies (depending on your sound equipment too!) than without it.
I’ve been doing most of my audio work with A/Demudi which is also a debian that has been highly optimized for this purpose. Like a Ferrari it is very fast and very good at what it does. Like a Ferrari it is also very difficult to just drop extra modifications on to without degrading it’s performance in one way or another (or simply breaking it!). Hence my recent attempts to coax a more general use distro (Kubuntu/Ubuntu, in this case) into the world of realtime audio work.
This has been an ongoing quest of mine for some time and I’ve experimented with Mandrake, Fedora Core, and several other debians including Mepis, Kanotix, and previously Ubuntu with little success. Finally I stumbled across a HowTo to get realtime running under Ubuntu 5.10 “Breezy”. The knowledge shared in the howto is common enough, for debian, and I’ve tried the methods in the past with earlier releases without success. This time it worked!
http://www.hardbop200.com/?page_id=6
Basically what it entails (although I highly recommend you read all of Hardbop’s excellent “howtos” in detail) is making use of the great debian tool “module-assistant”:
sudo -i
apt-get install linux-headers-$(uname -r)
apt-get install module-assistant
apt-get install jackd libjack0.80.0-dev qjackctl
m-a update
m-a prepare
m-a get realtime-lsm
m-a get realtime-lsm-source
m-a build realtime-lsm-source
m-a install realtime-lsm
NOTE: I DID have to install gcc-3.4 to get the m-a build sequence to work correctly. Your mileage may vary:
sudo apt-get install gcc-3.4
In summary this enables realtime access to the kernel for a regular user. You can test this by firing up jackd (try qjackctl) with “realtime” enabled. I’ve gotten my Maudio Delta 44 down to as low as 5.9ms of latency >without xrunssudo modprobe snd-seq
BUT this in itself has created a problem! With snd-seq enabled I do have full MIDI capabilities (two keyboard synths through a USB Maudio Midisport 4×4) but I can no longer get jackd to run in realtime mode! ~sigh~
Still going to try to get stuff running properly although my Demudi 1.2.1 install cdrom is looking pretty sexy over in my software rack…
Oktyabr's Notepad 
This is an amazing quick tutorial, but it even works with the latest Feisty build using the -realtime kernel. I now have realtime working on my system again and I never thought I would this easily.
Confirmed – I’ve used these instructions to get jackd running in realtime on both of my laptops (running Feisty). The only problem I ran into was that I had to run “m-a install realtime-lsm” twice. Both installation attempts claimed to have failed, but the “realtime” module was loaded and active after the second run.