Like the performances on the main release "GRIEG Piano Concerto", the bonus tracks for this album all derive from some form of perforated piano roll. The Humoresque and the Berceuse are the two remaining rolls that Grieg recorded for Ludwig Hupfeld in Leipzig in April 1906. He may have recorded more, of course, and the pile of rolls in the evocative photograph of Grieg listening to an unnamed Phonola player in 1907 in Berlin is tantalisingly unclear, but only six rolls were ever issued in Hupfeld's various catalogues. The Album Leaf and Puck are performances recorded by the Belgian pianist, Liszt pupil and long-term friend of Grieg, Artur de Greef, for the Aeolian Company's Duo-Art reproducing piano, the former in London in about 1920, and the latter in New York some ten years later. Grieg's own Duo-Art recording of Papillon (Butterfly) is more unusual, since the Duo-Art was not introduced until March 1914, nearly seven years after Grieg had died. The recording began life in Aeolian's Autograph-Metrostyle series, a non-recorded roll on which a tempo line had been drawn, under Grieg's own supervision, during a visit to Troldhaugen by George Reed of Aeolian in London. Although Aeolian never explained the process by which this tempo-marked roll was converted to Duo-Art, the likelihood is that it was pedalled, on an Aeolian 88-note Pianola attached to the Duo-Art recording piano in New York, by one of the American Duo-Art recording producers, who were in the main expert Pianola players as well.