'Masterly and full of new ideas'': thus the Swedish ambassadorial secretary Silverstolpe when he first heard these pieces in 1797. Haydn's friend, the music historian Charles Burney, reported in 1799 that he had ''never taken greater pleasure in instrumental music.'' Our new edition of these six works, including the famous ''Emperor Quartet,'' follows the text of the complete edition prepared by the Haydn Institute in Cologne. Both the study edition (HN 9214) and the set of parts (HN 214) have highly informative notes on the source materials and alternative readings. Fold-out pages in the parts allow for optimum page turns.?