You are most likely hearing a big difference in the enveloping (ADSR) of your sound patch (which certainly may have a profound effect on the duration of a keyed assigned note)
reasons are the ongoing saga of different assignment codes and sysex of GS vs XG vs I & II (Gen)
The external modulation codes for General differ from GS and Rolands rendition of General, as well as XG
This is the primary reason that many songs done as sweet as a popsicle in one MIDI layout can become smelly poopsicles in other MIDI formats. You see , it's enough to make you feel like your groove is mounted on a weak and sagging coil spring (that's not really too good)
Trust me maestro, we are all dying to just go out and buy a "plug it into me, I will sort it out for you, I'm a know all formats box". Funny, you know the maestros at MOTU were boiling such a creature at one time in the quite distant past. I guess after it was refined into a device it turned out to be not it's intention, and nobody is going to knowingly mass produce a Frankenstein, hence "ine vondabox" remains a figment of the imagination- comprende?
Unfortunately, this imaginary box shall remain just that too; only imagined. The reason I believe are the seeming like forever changes being made to these formats.
Personally, I think MIDI was originally approached totally wrong. I believe the base transmission should have been along a parrellel symantic, or well for all the goodness! not a serial one anyway! Not a single format currently out there that doesn't have to hurry up and wait as a normal proccess. One thing I know for sure, and that is that the original person who devised MIDI into existance was no maestro of music.
Petey
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MORPH! Sound