[LAD] automation on Linux (modular approach)

[fons at kokkinizita.net]

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,

-- 
FA

O tu, che porte, correndo si ?
E guerra e morte !