Kauffmann's prelude to ``Ach Herr, mich arme Sünder'' is a simple yet attractive bicinium. Well, I say 'simple', writing an attractive simple bicinium is never simple. The music nicely alternates between E flat major and c minor (or perhaps better: g phrygian), leaving the listener to wonder which of the two Kauffmann will chose for the end of the piece.
The recording was done with the Hauptwerk software and the sample set of the Vermeulen organ of Sts. Simon and Jude Thaddeus Apostles Church in Raszczyce by Piotr Gabrowsky (http://www.piotrgrabowski.pl/raszczyce.html)