f...@kokkinizita.net 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, >
Hi Fons :) could you please send me the test programs off-list. I made tests sending MIDI to a DX7. The DX7 generated an extremely short sinus impulse. I recorded it and examined the waveforms by Audacity. Btw. the graphics has access to the main memory, unfortunately it's a shared RAM, OTOH I used HPET so unwanted interrupts because of a shared RAM shouldn't be the cause, if I do understand the workings of HR timers correctly. Cheers! Ralf _______________________________________________ Linux-audio-dev mailing list Linux-audio-dev@lists.linuxaudio.org http://lists.linuxaudio.org/listinfo/linux-audio-dev