Regular it shifted between 2395 and 2404, but with a few exceptions, one time 2302, three times 2304, two times 2305 and two time 2494. See attachment. What might cause this exceptions? Could it be access to the RAM by the graphics? Is there something bad because of the IRQs? Regular shift 2404 - 2395 = 9 frames of jitter, exceptional maximal shift 2494 - 2302 = 192 frames of jitter. I guess this does mean ... 5.3 ms / 512 frames = 0.010351562 ms/frame Maximal difference for regular jitter 0.093164062 ms. Maximal difference for exceptional jitter 1.9875 ms. ... am I wrong? When I once tested it by recording I got this result for ALSA MIDI on Linux, Cubase runs on Windows on the same machine: ||Cubase|HR tmr|System|PCM pl|PCM ca ------++------+------+------+------+------ 500.0 || 493.0| 504.9| 505.6| 503.4| 503.2 1000.0|| 993.4|1005.4|1005.8|1005.3|1006.4 1500.0||1494.5|1503.6|1506.4|1507.4|1507.3 2000.0||1994.8|2003.8|2007.2|2007.9|2009.5 2500.0||2492.4|2504.1|2504.3|2503.6|2503.2 3000.0||2992.9|3006.0|3006.2|3005.9|3007.6 3500.0||3493.7|3502.7|3505.4|3506.5|3509.5 4000.0||3994.6|4003.1|4003.2|4008.8|4009.9 msec +/- 0.1 msec maxDif|| 4.8| 6.0| 7.2| 8.8| 9.9 minDif|| -2.4| -2.7| -3.2| -3.4| -3.2 --------------+------+------+------+------ Jitter|| 2.4| 3.3| 4.0| 5.4| 6.7 msec +/- 0.2 msec It's impossible to make music using external MIDI equipment and ALSA MIDI on my machine and for Windows it isn't really much better. While the test using Fons apps resulted with 1.9875 ms (if I understand it correctly) for JACK MIDI, my tests resulted with 4.0 ms for the system timer using ALSA MIDI. If you play one drum sound after the other using hardware MIDI and you record one sound after the other to audio tracks, than jitter needs to be less 2 ms. I don't know how much under 2 ms, but more than 2 ms is audible and sounds horrible. spinymouse-sudo@64studio:~$ hwinfo | grep irq [snip] irq:1 0 ( 133) "timer" irq:0 1 ( 7480) "i8042" irq:1 4 ( 3) "serial" irq:1 7 ( 0) "parport0" irq:0 8 ( 1) "rtc0" irq:0 9 ( 0) "acpi" irq:0 12 ( 300250) "i8042" irq:1 14 ( 28748) "ide0" irq:0 16 ( 1) "ohci_hcd:usb1" irq:0 17 ( 12747) "ohci_hcd:usb2" "ohci_hcd:usb5" irq:0 18 ( 2) "ohci_hcd:usb4" "ohci_hcd:usb6" "radeon@pci:0000:01:05.0" irq:0 19 ( 2) "ehci_hcd:usb3" irq:0 21 ( 246087) "ICE1712" irq:0 22 ( 23094) "ahci" "firewire_ohci" irq:0 25 ( 1925) "eth0" used irqs: 0,1,4,7,8,9,12,14,16,17,18,19,21,22,24,25 spinymouse-sudo@64studio:~$ uname -a Linux 64studio 2.6.31.12-rt20 #1 SMP PREEMPT RT Sun Feb 7 13:55:55 CET 2010 x86_64 GNU/Linux spinymouse-sudo@64studio:~$ cpufreq-selector -g performance spinymouse-sudo@64studio:~$ jackd -Rdalsa -dhw:0 -r96000 -p512 -n2 -Xseq jackdmp 1.9.3 Copyright 2001-2005 Paul Davis and others. Copyright 2004-2009 Grame. jackdmp comes with ABSOLUTELY NO WARRANTY This is free software, and you are welcome to redistribute it under certain conditions; see the file COPYING for details JACK server starting in realtime mode with priority 10 creating alsa driver ... hw:0|hw:0|512|2|96000|0|0|nomon|swmeter|-|32bit Using ALSA driver ICE1712 running on card 0 - TerraTec EWX24/96 at 0xcf00, irq 21 configuring for 96000Hz, period = 512 frames (5.3 ms), buffer = 2 periods ALSA: final selected sample format for capture: 32bit integer little-endian ALSA: use 2 periods for capture ALSA: final selected sample format for playback: 32bit integer little-endian ALSA: use 2 periods for playback port created: Midi-Through:midi/playback_1 port created: Midi-Through:midi/capture_1 port created: TerraTec-EWX24/96:midi/playback_1 port created: TerraTec-EWX24/96:midi/capture_1 port created: USB-Device-0x170b:0x11:midi/playback_1 port created: USB-Device-0x170b:0x11:midi/capture_1 ###################################################################### spinymouse-sudo@64studio:~$ cat /usr/src/jack_midi_test/jack_send.cc [snip] // This list of note on/off events is sent // in an endless loop, one item every DELTA // audio frames, on channel CHANNEL. // Note Notes [NNOTES] = { { 0x90, 48, 100 }, { 0x80, 48, 0 }, { 0x90, 50, 100 }, { 0x80, 50, 0 }, { 0x90, 52, 100 }, { 0x80, 52, 0 }, { 0x90, 53, 100 }, { 0x80, 53, 0 }, { 0x90, 55, 100 }, { 0x80, 55, 0 }, { 0x90, 57, 100 }, { 0x80, 57, 0 }, { 0x90, 59, 100 }, { 0x80, 59, 0 }, { 0x90, 60, 100 }, { 0x80, 60, 0 } }; [snip] spinymouse-sudo@64studio:~$ qjackctl ###################################################################### spinymouse-sudo@64studio:~$ /usr/src/jack_midi_test/jack_recv ###################################################################### spinymouse-sudo@64studio:~$ /usr/src/jack_midi_test/jack_send ###################################################################### Connected: jack_send out --> system midi_playback_3 system midi_capture_3 --> jack_recv in Results: 2400 2400 2401 2401 2400 2401 2399 2399 2400 2400 2399 2402 2400 2400 2400 2400 2400 2401 2398 2401 2400 2401 2400 2402 2399 2400 2399 2401 2400 2402 2400 2402 2396 2402 2399 2400 2401 2399 2402 2399 2400 2400 2399 2400 2401 2401 2399 2401 2399 2401 2400 2399 2401 2400 2400 2400 2401 2399 2400 2400 2400 2401 2400 2399 2402 2400 2400 2401 2401 2400 2399 2400 2400 2400 2402 2304 2494 2401 2400 2400 2398 2404 2398 2402 2399 2400 2400 2403 2398 2398 2402 2400 2401 2401 2400 2401 2399 2400 2400 2401 2401 2399 2399 2400 2401 2400 2401 2401 2401 2398 2400 2400 2400 2402 2400 2400 2398 2400 2401 2402 2401 2397 2400 2400 2400 2401 2402 2400 2399 2399 2401 2399 2402 2399 2400 2399 2401 2401 2398 2401 2401 2399 2400 2400 2400 2401 2401 2398 2401 2400 2401 2401 2401 2400 2399 2399 2400 2401 2400 2398 2401 2401 2399 2400 2401 2400 2402 2398 2400 2400 2400 2400 2402 2398 2401 2400 2402 2399 2399 2402 2399 2400 2400 2399 2403 2400 2399 2401 2401 2400 2401 2400 2398 2401 2400 2400 2402 2399 2400 2399 2401 2400 2401 2402 2398 2400 2400 2401 2400 2400 2401 2399 2400 2400 2400 2402 2399 2399 2400 2400 2400 2402 2400 2400 2400 2399 2400 2400 2402 2399 2399 2400 2401 2400 2400 2402 2399 2400 2400 2400 2402 2399 2401 2400 2399 2399 2400 2399 2403 2400 2399 2400 2400 2400 2401 2398 2403 2398 2401 2399 2402 2400 2401 2399 2399 2401 2400 2399 2402 2399 2399 2401 2401 2399 2402 2400 2399 2400 2400 2399 2401 2403 2398 2400 2400 2398 2404 2398 2401 2400 2400 2401 2400 2400 2401 2398 2399 2401 2400 2402 2402 2397 2401 2400 2400 2401 2400 2401 2398 2401 2400 2399 2402 2402 2400 2397 2402 2399 2402 2399 2400 2399 2401 2402 2399 2399 2399 2399 2402 2400 2402 2398 2402 2399 2401 2399 2400 2400 2403 2399 2399 2403 2302 2492 2309 2498 2399 2398 2304 2498 2401 2399 2399 2400 2401 2400 2401 2402 2397 2399 2305 2400 2402 2495 2399 2400 2304 2401 2400 2402 2494 2305 2400 2399 2401 2497 2302 2401 2400 2400 2400 2402 2401 2398 2401 2399 2400 2401 2402 2396 2403 2400 2400 2400 2401 2401 2398 2401 2400 2400 2402 2399 2402 2397 2401 2400 2401 2401 2399 2400 2400 2399 2401 2401 2401 2398 2401 2400 2400 2401 2402 2402 2396 2400 2400 2400 2403 2398 2400 2399 2402 2399 2402 2400 2399 2400 2399 2401 2401 2402 2398 2399 2400 2400 2401 2401 2400 2400 2399 2400 2400 2402 2401 2403 2395 2400 2400 2400 2400 2400 2400 2399 2401 2400 2400 2400 2402 2399 2399 2400 2401 2400 2399 2403 2399 2399 2400 2399 2403 2401 2397 2402 2399 2401 2400 2399 2404 2397 2401 2399 2402 2400 2402 2396 2402 2399 2400 2401 ^C spinymouse-sudo@64studio:~$