The Notalium Tuner is what allows Fisica and Ritmo to restore life to the world, as well as the player interface for Lanota. It appears as a bowl-like object with keys in the Items menu, and as a wheel painted in either blue or red and gold while playing songs.
Fisica designed and built the Notalium Tuner using blueprints from the Notalium Administration, according to the Items menu. Nothing is said about where the blueprints came from or who made them in the first place - only that the Administration kept them safe over the years.
The Notalium Tuner reactivates the energy within Notalium crystals, putting it back into its ordered, usable state. This plays a melody as stated after playing Chronosis song or Eternal Love, which makes sense seeing as Notalium is sound put in crystals.
The Tuner also features two modes for restoring the crystals' energies - Tune and Purify. While both of them do the job of taking Notalium out of its disordered state, Purify is the only option for reactivating/stabilizing crystals with very strong energy. It's also a function Fisica says is "still under development" when accessing the Cave for the first time. The two modes can be told apart by what color the Tuner is while playing a song (blue for Tune and red for Purify).
In addition to tuning Notalium, Fisica added a detecting mechanism to the Tuner in Chapter 1's intro so as to "[give] their mission direction". It also has an alarm that sounds when tuning awakens unstable crystals (such as those in the Clock Tower). This alarm is a high-pitched beeping noise.