With your midi playback drivers, you also want to have a
Soundfont for the mandolin installed on your computer. There are many of these soundfonts out there, in large packages of sound fonts for all sorts of instruments. Do a Google search on "
Soundfont mandolin." You'll find lots of stuff.
If you don't do that, you can always fall back to using a steel-string guitar as the playback instrument, which is found in the Windows standard midi instruments. The mandolin range will use the higher octave on the guitar, of course. This sounds OK, but not great.
Here are some links to libraries of soundfonts:
http://www.synthfont.com/links_to_soundfonts.html
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