Friedrich Wilhelm Marpurg, Ach Gott und Herr
Marpurg’s prelude to the chorale “Ach Gott und Herr” is again a case of two compositions tolled into one. As it were, two preludes for the price of one. The first one features the choral melody in the middle voice. To make it more easily recognizable, that middle voice can be played with a solo stop on the pedals. In my performance I choose to play as a manualiter piece. That makes the chorale melody a little harder to follow, yet it is there and if you concentrate a little you should be able to follow it from beginning till the end.
Marpurg writes a lively accompaniment for this first half. The outer voices introduce the piece with four bars of music, that form an important building block for the rest of the compositions. Those four bars return between each of the phrases of the choral melody. The music is transposed to other keys and the melodic lines of both hands turn out to change position: what is first played with the right hand becomes the melody for the left hand and vice versa.
The second half of the composition is bit more bland in comparison. The choral melody is played in the upper voice and the two lower voices play the accompaniment. No refined motivic play in this half of the composition, but rather a functional motoric accompaniment.
The recording was done with the Hauptwerk software and the sampleset, made by Sonus Paradisi, of the Schnittger organ in the St. Martini-kerk, Groningen (https://www.sonusparadisi.cz/en/organs/netherlands/groningen-st-martini.html).