Using inelastic x-ray scattering and parameter-free calculations the authors provide the first complete and fully consistent lattice dynamics description of MgSiO3-brigmanite, the main constituent of the Earth’s lower mantle and one of the most important Earth’s minerals. The present work constitutes an important milestone fully validating the lattice dynamics calculation against precise experimental evidence and marks a starting point to extend this kind of combined studies to the high-pressure and high-temperature conditions directly relevant for the physical properties and chemical composition of Earth's lower mantle.