It doesn't matter if they are note-off or note-on with a velocity=0, fluidsynth treats both as note-off events.  You are experiencing a bug which occurs when a note-on is followed shortly by a note-off or note-on-velocity-zero event.  If the temporal spacing between the two events is short enough that fluidsynth processes both events during the same cycle, then audio for the note-on is never generated.  This occurs most frequently with percussion tracks since the note-on and note-offs are spaced very closely together.   The only solution I've found is to strip out the note-off events in the percussion tracks altogether.   Its a pain, but works pretty well.

Ken

--- On Thu, 9/10/09, James Cameron <quozl@us.netrek.org> wrote:

From: James Cameron <quozl@us.netrek.org>
Subject: Re: [LAU] FluidSynth fails to sintetize more 85% events generated by Drum machine ALESIS D4.
To: linux-audio-user@lists.linuxaudio.org
Date: Thursday, September 10, 2009, 4:10 PM

On Thu, Sep 10, 2009 at 07:36:06PM +0200, Jedi Storm wrote:
> MIDI Keyboard or Virtual Keyboard generate NOTE ON and NOTE OFF events , The
> alesis D4 only generates NOTE ON midi events.

This will be the cause of the symptom.

Change the D4 configuration to generate NOTE OFF events?

I've checked, and fluidsynth has no documented option for inventing the
NOTE OFF events, so you have to generate them.

I've briefly googled, and there are mentions of changing the D4 to
generate NOTE OFF events.  I'm not familiar with the D4 myself though.

--
James Cameron
http://quozl.linux.org.au/
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