Friedrich Wilhelm Marpurg (1718 – 1795) was a German music critic, music theorist and composer. During his life he published two volumes of chorale preludes, which contain his only known composition for the organ. The Bayerische Staatsbibliothek provides digital copies of these two collections of chorale preludes. The second one is sadly incomplete so we are left with some fragments of pieces of music that could be worthwhile to play if the were complete. Best not to dwell too much on that.
The prelude on the melody of "Ach was soll ich Sünder machen" is the second composition from the first collection. It features the chorale melody in canon, played with the right hand. As the melody of this chorale consists of descending lines (except for the first line of the melody) it is inevitable that the voices cross each other. The original publication tries to resolve this by changing the order in which the two voices enter: first the soprano in the first line, in the remaining lines first the alto voice. However that leads to strange to look at voice crossings in the second half of each of these lines. I think the score is more easy to read when the soprano voice consistently enters first. So that is how I typeset it.
The recording was done with the Hauptwerk software and the sampleset, made by Sonus Paradisi, of the Schittger organ in the St. Martini-kerk, Groningen.
Score available here: http://partitura.org/index.php/friedrich-wilhelm-marpurg-ach-was-soll-ich-sunder-machen
