[LAD] automation on Linux (modular approach)

[Tim E. Real]

On March 24, 2010 05:59:53 pm fons at 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,

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.