I'm orchestrating a piece I've written and realized the thing that bothers me most about the brass (not just GPO) is the release. As a trumpet player I was taught early on that for classical music the release is an 'open-ended' release. Unlike commercial brass playing where you stop the sound with your tongue you simply stop blowing, but the tongue stays out of the way.
I haven't figured out how that translates to samples though and in particular GPO. When the midi note off is sent, it sounds like a very abrupt ending as if the player is stopping the note with his/her tongue. Is there a solution for this that anyone has found?