Musik in Geschichte und Gegenwart: Article "Organ chorale"
Excerpt: "... Johann Sebastian Bach's work was essentially based on the chorale arrangement types developed in central Germany...
Under Bach's hand, however, the traditional chorale arrangement types changed fundamentally due to the new importance that the contrapuntal voices now had: they now stand opposite the chorale melody, whether they are freely designed or derived from the material of the cantus firmus..."
(Prof. Dr. Arno Forchert, Rudolf Innig)