Instruments are the Bard’s version of focus effects, basically they make the song better (i.e., you will run faster, your dots will hit for more, etc). There are a few songs such as ‘Shauri’s Sonorous Clouding’ (invis song) and ‘Alenia’s Disenchanting Melody’ (group dispell) that require an instrument (or item with instrument modifier) to be equipped. There are also a few songs like our slow that are not effected at all by instruments.