The transcription process was a common practice during the Baroque era, where composers frequently adapted and rearranged works by their contemporaries or predecessors. In the case of BWV 596, Bach not only transcribed the original work but added his ownartistic touches.
In this publication, Michael Forbes takes Bach's organ transcription and adapts it to the euphonium/tuba quartet. Brass ensembles have the advantage of being able to easily imitate the sound of the organ in its various registers. -the publisher