Possible Clues:

• Line up
• Come together regularly, say, in act
• Say, an act with nothing even in harmony
• Out of ___ (not harmonized)
• Coordinate, as a Mac and iPhone
• By the sound of it, go lower in harmony
• Work together with extremely savvy neurotic
• Match, like audio and video
• In __ (well-coordinated)
• In ___ (with matching audio and video)