14 Jul
2010
14 Jul
'10
11:38 p.m.
On Wed, 2010-07-14 at 14:12 -0700, Devin Anderson wrote:
On Wed, Jul 14, 2010 at 12:43 PM, Ralf Mardorf
<ralf.mardorf(a)alice-dsl.net> wrote:
Should I build JACK dummy packages for 64 Studio and daily get JACK2
from svn co http://subversion.jackaudio.org/jack/jack2/trunk/jackmp ?
I wonder if this should be cross-posted to LAD?
On LAD and the 64 Studio list are people with much knowledge and your
reply might hit the nail on the head.
- Ralf
On Wed, 2010-07-14 at 12:30 -0700, Devin Anderson
wrote:
If it ends up being the case that your MIDI device is being triggered
before your software synth, then I'm guessing that the issue here is
not MIDI jitter. I'm guessing the issue is that the latency that's
imposed by JACK on incoming and outgoing audio is not imposed on
incoming and outgoing ALSA MIDI. So, while the audio coming out of
the software synth is delayed by a certain amount of frames imposed by
JACK, the audio coming out of your MIDI device is only delayed by the
latency of the ALSA drivers, the latency of the MIDI ports, the
latency of your MIDI device.
This would certainly explain why the problem gets worse as you raise
the period size, and could explain why you had positive and negative
delay in your older USB MIDI tests, as the reported MIDI jitter in
your tests was *far* worse in your older tests than it is now.
At the moment, I happen to be doing some work in JACK 2 that could
potentially solve this issue by enabling MIDI to sync more closely
with audio, so I'm very curious to know if my suspicions are correct.
Please keep me updated. :) On Wed, Jul 14, 2010 at 10:29 AM, Ralf Mardorf
<ralf.mardorf(a)alice-dsl.net> wrote:
Yes :).
Hi :)
delayed by a thunder-storm I could do another test.
--snip--
So, what you're saying is that your MIDI device and software synth
sync up less and less as you raise the period size. I had presupposed
before that your MIDI device was triggering *after* your software
synth, but it occurs to me that it might be the other way around. Do
you hear the audio from your software synth first, or from your MIDI
device?
I can't say it today, now I do some office work. I had the impression
that it might vary. Sometimes the virtual drum sampler and sometimes the
standalone drum sampler was played earlier, I need to check this ASAP.
For older tests with my USB MIDI device it was exactly that way, that
jitter had positive and negative delay. At least the recorded waveforms
of external MIDI equipment (when I used USB MIDI, now I'm using PCI
MIDI), were recorded by Qtractor, before theoretically the MIDI event
was send ;). Note! Qtractor had no latency compensation, all recorded
audio of external MIDI instruments should have (positive) delay, but
negative delay.