You may play up to two bardic magic songs at the same time.
Without this ability, you can only play one bardic magic song at a time.

Continuing Multiple Songs:
At the start of each of your turns, you may attempt a test to perform each bardic magic song that you are playing to continue it until the start of your next turn. If you fail, or choose not to continue the song, that song ends.
Each song that you are playing must be successfully continued at the start of each of your turns, or that song ends.

You cannot perform the same bardic magic song multiple times simultaneously.

When you spend an action starting a bardic magic song,
you may also start an additional song without spending an action.

While you are only playing one bardic magic song,
its numerical effects are increased by their base value.

(ex: A One Hit Wonder Bardic Performance would give you and your allies
a +2 to hit and tests of skill instead of a +1,
and you a -2 to tests of Roguery to hide instead of a -1.)

You cannot use One Hit Wonder on downtime rolls.