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-   -   Correlation of alsa -p value and hw MIDI jitter (http://www.linux-archive.org/64-studio-user/399324-correlation-alsa-p-value-hw-midi-jitter.html)

Devin Anderson 07-14-2010 07:30 PM

Correlation of alsa -p value and hw MIDI jitter
 
On Wed, Jul 14, 2010 at 10:29 AM, Ralf Mardorf
<ralf.mardorf@alice-dsl.net> wrote:

> 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?

--
Devin Anderson
devin (at) charityfinders (dot) com

CharityFinders - http://www.charityfinders.com/
synthclone - http://synthclone.googlecode.com/
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Ralf Mardorf 07-14-2010 07:43 PM

Correlation of alsa -p value and hw MIDI jitter
 
On Wed, 2010-07-14 at 12:30 -0700, Devin Anderson wrote:
> On Wed, Jul 14, 2010 at 10:29 AM, Ralf Mardorf
> <ralf.mardorf@alice-dsl.net> wrote:
>
> > 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.

Yes :).

> 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.

- Ralf

PS: Today I just listened to similar sounds and didn't notice if there
was negative delay or what drum sample might be played before the other,
I just noticed that they were not played in unison.

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Ralf Mardorf 07-14-2010 07:43 PM

Correlation of alsa -p value and hw MIDI jitter
 
On Wed, 2010-07-14 at 12:30 -0700, Devin Anderson wrote:
> On Wed, Jul 14, 2010 at 10:29 AM, Ralf Mardorf
> <ralf.mardorf@alice-dsl.net> wrote:
>
> > 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.

Yes :).

> 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.

- Ralf

PS: Today I just listened to similar sounds and didn't notice if there
was negative delay or what drum sample might be played before the other,
I just noticed that they were not played in unison.

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Ralf Mardorf 07-14-2010 09:38 PM

Correlation of alsa -p value and hw MIDI jitter
 
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@alice-dsl.net> wrote:
> > On Wed, 2010-07-14 at 12:30 -0700, Devin Anderson wrote:
> >> On Wed, Jul 14, 2010 at 10:29 AM, Ralf Mardorf
> >> <ralf.mardorf@alice-dsl.net> wrote:
> >>
> >> > 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.
> >
> > Yes :).
> >
> >> 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.
>
> 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. :)

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


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Ralf Mardorf 07-14-2010 09:38 PM

Correlation of alsa -p value and hw MIDI jitter
 
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@alice-dsl.net> wrote:
> > On Wed, 2010-07-14 at 12:30 -0700, Devin Anderson wrote:
> >> On Wed, Jul 14, 2010 at 10:29 AM, Ralf Mardorf
> >> <ralf.mardorf@alice-dsl.net> wrote:
> >>
> >> > 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.
> >
> > Yes :).
> >
> >> 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.
>
> 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. :)

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


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Ralf Mardorf 07-14-2010 10:04 PM

Correlation of alsa -p value and hw MIDI jitter
 
No firewire here. I once had a MOTU, but I guess that there isn't a
driver for Linux and the guy who lend me the MOTU + Mac was Dirk Brauner
who isn't a friend anymore. I guess the MOTO was audio only. The people
who are still my friends don't have much different equipment, but I've
got. Always Envy24 based PCI, one friend has just more IOs for his
Envy24 based PCI card.

> Make sure that the MIDI device is being triggered before the soft
> synth before you post to LAD. If it ends up being the case, then go
> ahead and post it on LAD.

You're right I was stupid to spread to much speculations.

And yes, regarding to your knowledge you should join LAD.

- Ralf


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Ralf Mardorf 07-14-2010 10:04 PM

Correlation of alsa -p value and hw MIDI jitter
 
No firewire here. I once had a MOTU, but I guess that there isn't a
driver for Linux and the guy who lend me the MOTU + Mac was Dirk Brauner
who isn't a friend anymore. I guess the MOTO was audio only. The people
who are still my friends don't have much different equipment, but I've
got. Always Envy24 based PCI, one friend has just more IOs for his
Envy24 based PCI card.

> Make sure that the MIDI device is being triggered before the soft
> synth before you post to LAD. If it ends up being the case, then go
> ahead and post it on LAD.

You're right I was stupid to spread to much speculations.

And yes, regarding to your knowledge you should join LAD.

- Ralf


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