Dynamic brain macrostructural and microstructural changes occur from mid-fetal stage to birth. Prematurity disrupts brain maturation during this critical period and music might enhance activity-dependent-plasticity during early brain development. Using a longitudinal fixel-based analysis, we evaluated preterm brain macro and microscopic fiber changes from 33 weeks to term-age and the impact of music, during neonatal unit stay, on these changes. We show that fiber density (FD) and fiber-bundle cross-section (FC) increase in all major white-matter fibers over time, while in the cortex FD decreases and FC increases. Music intervention lead to a significant cortical FC increase in comparison to standard-of-care.