Terminology:
RealTracks are studio recorded sessions of audio that BiaB/Realband can slice/dice to make songs.

MIDI - digital messages that get sent to a synth or FX (they contain no sound themselves; the synth creates the sound based on the message it receives). Musical Instrument Digital Interface

Realband - the 48 track DAW that comes with BiaB and has the ability to use the BiaB engine for both MIDI and Realtracks.

Knowing the above may help clear up your questions.

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