Thanks Mario, Videotrack and Cooltouch. I've got a solution. As you explained, I can use MIDI CC 11 (Expression) to control the volume within the duration of the note, and that appears to work just fine. I've attached a screenshot of how I would use it on a particular note. I discovered by accident that you can just drag the mouse cursor across a range it will create a descending line.

I'm still a but puzzled though because I tried to determine using both MIDI monitor and the Step Edit feature in the Edit Melody Track option to find out what MIDI command was providing the fading effect on the guitar notes, but was unable to. The MIDI monitor seems particularly problematic on my system - it appears to drop a lot of events, even when I filter just one channel. That may be a topic for another post.

In any case, thanks much gentlemen. I have a solid solution.

Attached Files (Click to download or enlarge) (Only available when you are logged in)
Ed Z

Soundcloud profile
https://soundcloud.com/user-415064494
BIAB user since 2019
iPad Mini, Garageband for iOS, BIAB for Windows 2020 UltraPAK, Xtra Styles packs 6-9, Windows 10 Lenovo PC, Kontakt Player, SpitFire LABS, SampleTank 4 CS, some Soundfonts