 His research on Beethoven's symphonies started in 1984.In December 1996 the score for the Ninth Symphony was published, attracting attention from the press.There were four recordings of the symphony prior to the publication of the new edition, with the conductors using the Breitkopf edition with the corrections as they were available to them; Roy Goodman was the first conductor using corrections by Del Mar, followed by Sir Charles Mackerras in 1991, Sir John Eliot Gardiner in 1992, and Claudio Abbado in 1996.