this backing track is:
for Bass

it is in the key of:
Bb (concert)

arrangement:

Drums start – 1,2,3,4, 1,2,3, First note of melody begins on fourth beat.
(Follow the chord chart exactly)
Once through the tune (32 bars)
Key changes (up a 4^th) for 8 bars
Back to original key (don’t be confused - the first chord of the last 16 bars is a 4^th up, then resolves on second bar)
The final resolving chord is Dmaj7 (concert).

Refer to chord charts.