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Riker was a jazz aficionado
and his favorite musical instrument was the trombone. Although he was an accomplished player, his skills were not quite up to that of a professional musician (TNG: "11001001") and he had trouble with certain pieces, including Nightbird. (TNG: "Second Chances")
In reality, Jonathan Frakes is a trombone player and provided the audio whenever Riker was shown playing. Riker was also shown playing the trombone in TNG: "Future Imperfect", "The Next Phase", and "Thine Own Self".
http://trombonist.files.wordpress.com/2007/04/riker.jpg
RIKER