alsa_midi timing

[tim]

Hi all,
 
Last week I tried to play a soundfont in Qsynth from Pd.
They connect via alsa_midi (I make settings with qjackctl).
The timing is very irregular, and the notestream is sometimes 
interrupted by gui activity.
Seq24>alsa_midi>qsynth produces similar results, as does 
Rosegarden>alsa_midi>qsynth...
The test I did was simply repeat the same sample every 100 miliseconds. 
(note on, 50ms, note off, 50 ms)
Hardware specs: amd 2.6ghz, 2gig ram, rme hdsp soundcard.
I am running ubuntustudio with low-latency kernel.
in Jack: RT on, Priority 30, 96000kHz.
Larger buffersizes reduce interruptions of audio, but the midi timing 
remains lousy.
How do you get steady midi timing ?

Thanks in advance,
Tim