This choral prelude is also known as "Ricercar pro Festis Natalytis". Carl Philipp Emanuel Bach wrote that his father considered Fischer to be one of the greatest composers of his time. This ricercar can help to understand why. It is a very cleverly constructed fugue on the first line of "Der Tag der ist so freudenreich". The recording was done with the Hauptwerk software and the sampleset, made by Sonus Paradisi, of the Bader organ in the Walurgiskerk, Zutphen. Free score available here: http://partitura.org/index.php/johann-caspar-ferdinand-fischer-der-tag-der-ist-freudenreich/