Ballad of Battle

You inspire your allies through song creating an aura of rousing music that extends 30 ft from you and moves with you. The aura grants friendly creatures in the area that can hear you a +1 bonus to attack rolls. Once per round as a reaction you can grant advantage to an attack a friendly creature makes in the aura on their turn. You must use this reaction before the attack hits or misses.

At higher levels when you cast this spell using a slot above 1st, the advantage granted also causes the attack to deal an additional 1d8 thunder damage per level of the spell. Additionally the attack bonus increases every 3rd level, to +2 at 3rd, +3 at 6th, and +4 at 9th level.