Society heraldry accepts as charges those musical instruments known before 1600, and a wide variety have been registered. In some cases the blazon makes a distinction purely for the artist’s sake; there is no heraldic difference between, e.g., a rebec and a gittern, and it would take a medieval musicologist to tell them apart. When in doubt, it’s best to be general, rather than specific: e.g., “fiddle” instead of “viola da braccio”.
In general, musical instruments are affronty by default, with the strings or fingerholes facing the viewer. For specific entries, see: bagpipe, bell, clarion, cornetto, drum, flute, gittern, guitar, harp, hautboy, horn (hunting), hurdy-gurdy, jew’s-harp, krummhorn, lute, lyre, organ pipe, panpipe, portative organ, psaltery, rackett, recorder, sackbut, sitar, trumpet, viol, whistle (mariner’s), zil, zither.