Kommentare zu: Making Music with Linux

Von: ekkehard

ekkehard — Sat, 06 Mar 2010 16:25:54 +0000

OK, “timidity -B10,8 -Oj -iA” gives OK timing for my machine when Rosegarden is running.

Ahhh … looks like I’m finally getting somewhere!

Von: ekkehard

ekkehard — Sat, 06 Mar 2010 16:22:41 +0000

Now I discovered that timidity is using ridiculously large buffers by default, which was the audible delay that I perceived. When running timidity with “timidity -B10,7 -Oj -iA” then there’s absolutely no perceivable delay.

When Rosegarden runs, there’s some choppiness in the output, however … I yet have to figure that one out.

Von: ekkehard

ekkehard — Sat, 06 Mar 2010 15:33:22 +0000

OK, so after much more fiddling with that … stuff … , I found out that timidity and jackd were in competition about the ALSA outputs. I uninstalled the “timidity-daemon” package, which simply removes the init.d script, and ran “timidity -Oj -iA” from the command line when jackd was running on ALSA. Important configuration options for jackd in Jack Control are setting the frame size down to 256 from 1024 and setting the realtime priority up from default to 10. To run jackd in realtime mode, it is necessary to configure the PAM security manager in Ubuntu. This can be done by editing “/etc/security/limits” as described in the jackd FAQ (at http://jackaudio.org ).

Still, my impression is that using Jack is degrading performance to a degree since there’s now some perceivable latency that wasn’t there before when only ALSA MIDI was being used without Jack.

Anyhoo … at least now both wave audio and MIDI can be used at the same time.

Von: ekkehard

ekkehard — Sat, 06 Mar 2010 13:58:37 +0000

lol, I just figured out that jackd isn’t actually running at all when using the “sudo /etc/init.d/jackd start” command. It prints OK but the daemon is not running. (”Stopping” the daemon also prints OK.) However, a PID file is written that makes applications like Rosegarden think that jackd is running. In fact, only ALSA MIDI is being used. Sometime I need to figure out how to set this up properly, lol! At least MIDI is working like that.

Von: ekkehard

ekkehard — Sat, 06 Mar 2010 13:08:08 +0000

In any case, these problems may lead to a complication in audio production workflow: You may have to record the MIDI tracks separately, capture the audio using an audio recording program, and then use tools like Audacity to post-process the wave audio (or import them into a new project using only wave audio).

Von: ekkehard

ekkehard — Sat, 06 Mar 2010 13:04:57 +0000

Furthermore, if you don’t run jackd as daemon, and run it user mode using the Jack Control Start button, then MIDI apparently doesn’t work (at least the connection between Virtual Keyboard and the timidity daemon produces no audible output; this also happens when timidity doesn’t run as a daemon). Conversely, if you do run jackd as a daemon, then the audio connectors for wave audio won’t appear in Jack Control, however, MIDI does work in that case. Since I’m only interested in MIDI at the moment, that’s no problem for me. I think it has to do with the fact that Ubuntu configures GNOME to use PulseAudio exclusively (despite there seems to be no obvious correlation between PulseAudio and these problems).

Von: ekkehard

ekkehard — Sat, 06 Mar 2010 12:49:38 +0000

I discovered a nasty bug in either the jackd init script or jackd: When you run jackd at boot time, it apparently crashes without removing its pid file. Anyway, you have to start the daemon manually after every reboot using “sudo /etc/init.d/jackd start” to get things running. Also, DON’T click on the “Start” button in Jack Control, b/c Jack Control apparently doesn’t know about the possibility of running jackd as a daemon. In the Jack Control configuration, uncheck the starting of scripts and uncheck the realtime option. Avoid clicking on the Start button. If jackd runs as a daemon, it’s not necessary to click on it.