just to add to the excellent explanation by Matt the manual provides this information

" RealTracks are audio instruments that replace the MIDI track with actual recordings of top studio Jazz/Rock/Country musicians! These are not “samples” of single instrument hits; they are full recordings, lasting from 1 to 8 bars at a time, playing along in perfect sync with the other Band-in-a-Box tracks. "

the manual is built into the Band programme and can be read by going to the " Help " see my screen shot

hope this all helps you

Mister Magoo/w

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Mac Audiophile 2020 2019 2018 2017 USB plus previous years versions

macOS Mojave - 10.14.6 @ Aug 16, 2019

iMac i3 3.6 GHz 8GB RAM 4K with Retina display

some examples @ sound cloud done with Mac Band and DAW's : https://soundcloud.com/you/tracks