On March 24, 2010 05:59:53 pm [email protected] wrote: > On Wed, Mar 24, 2010 at 11:06:43AM +0100, Ralf Mardorf wrote: > > At the > > moment Linux on my computer and on computers of around 30 other people I > > know can't use hardware MIDI equipment because of MIDI jitter. On the > > same machines there is less jitter for Windows, so using Windows would > > solve this problem for most of them. > > This made me curious, and as I rarely use MIDI (just > to play piano using Linuxsampler) I wrote two trivial > test programs usin MIDI over Jack. > > The first will output a note on or off every 10 ms. > The second just receives midi a prints the time > (number of frames) since the last event for each > one received. > > When connected directly via Jack the result is a > boring series of '480', one event each 10 ms. > > When connected via a loopback on a HW interface > I expected the worst case to be events quantised > to Jack period (256 frames). Actually it's 10 times > worse - events are bunched into groups, one for > every 10 periods. That 53 ms of jitter or if you > are optimistic, +/- 26 ms. > > The interface used is PCI based, no USB problems. > > What is going one here ? > > Ciao,
This concerns me greatly. Wow, long thread, way off topic, but sorry I must ask... I recently added Jack midi to MusE-1. I borrowed some Jack midi code from MusE-2. In one section, the original author made some accommodation for 'jitter'. I didn't understand what it was about, so I left this part out of MusE-1. IIRC it appeared to delay all the notes by one Jack period, or something like that, to counteract jitter. I didn't want to introduce that delay, so I left it out. Am I going to have trouble? What's at fault with this jitter? Must be ALSA? Can we elaborate some more on this this 'jitter'? What can be done? Thanks. Tim. _______________________________________________ Linux-audio-dev mailing list [email protected] http://lists.linuxaudio.org/listinfo/linux-audio-dev
