How do Freestyle Vocals work in Rock Band 4?

You can only play with Freestyle Vocals in Rock Band 4 if you are on Hard or Expert difficulty. Freestyle Vocals allow you as the player to sing "outside the box" - you will be scored for accurately singing the harmonic chord tones that are associated with each changing chord in a song. Giving you the ability to express yourself in new and exciting ways, this feature will allow you to really tune in with the musical structure of each track.