The prelude on folio 33 of manuscript Mus Ms Lynar B3 bears the initials M.D.O. The preceding prelude bears the initials "A.D.O" which are believed to stand for the composer Andreas Düben, and the title "Organista". If that is true than what does "M.D.O" stand for? In "The History of Keyboard Music to 1700" (Indiana University Press, 1972) Willi Apel writes that the "M" may well mean "Magister", but that it might conceivably stand for another given name, such as that of an otherwise unknown brother of Andreas. Since then evidence of that unknown brother must have been found, because this prelude is now believed to have been written by Martin Düben, of which even a year of birth and death are given: 1598/99 - 1648. There is not kuch known about this Martin Düben. He was probably, just like his brother Andreas, a pupil of Sweelinck. Later in live he moved to Stockholm and became organist there.
The prelude itself is a simple, charming work. Whoever wrote it, it was a job well done.
Score available here: http://partitura.org/index.php/m-d-o-martin-duben-praeambulum-pedaliter