From Final Fantasy Wiki

Operetta is a song available to Bards in Final Fantasy XI.

There are two versions of Operetta. The first, Scop's Operetta, protects all party members within range from Silence. This effect is similar to, but stacks with, Barsilencera. The second, called Puppet's Operetta, is available only at level 69 and protects against Silence and Charm effects.