Why do Bards need Instruments?

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.