Phonic gain is the most basic principle of the Symphogear system. By using the power of song, a potential candidate provides power to their Symphogear.
However, this principle has also been used by non-natural candidates, and it is when that happens that abilities like the X-Drive can be unlocked.
In Episode 12, the phonic gain produced by all of Hibiki's friends singing the Shiritsu Lydian Ongakuin Kōka was enough to revive Tsubasa Kazanari and Chris Yukine after they had died, give Hibiki the strength to keep fighting, and unlock the X-Drive for all three of them.
In Season 2, Episode 13, the phonic gain produced by the whole world was used to reactivate the Lunar Ruins, thereby preventing the Moon from crashing into the Earth, as well as allowing all six Symphogear users to activate the X-Drive.
In Season 3, Episode 13, the phonic gain produced by the song of Carol Malus Dienheim, which had the same power as 7,000,000,000 Superb Songs, was used together with the S2CA Hexa-Convergence to once again allow all six X-Drives to be unlocked.
- Some fans have theorized that a user can feed off phonic gain while another is singing in battle.
- Phonic gain normally looks like yellow orbs of light. But when powerful, it looks like a large yellow cone.