For Add-ons
Each add-on has a soundtrack.
In-Game
The music will play in game, and a toast in the bottom-right corner will say the track. Music discs, music for new/my biomes, add more music to existing/vanilla biomes
Music Discs
These items resemble music discs and are put in a Boombox as to not replace music discs. There are music disc exclusive songs and also all biome songs have music discs too.