Choose the Hi-Res Audio product type when creating a new product. All MFiT audio assets must be 44.1KHz/24 bit or 96KHz/24 bit quality or will be rejected on upload. The same quality must be uploaded for every track on a given release.
iTunes also requires that MFiT products follow specific mastering guidelines, including being mastered by iTunes-approved mastering studios. Contact firstname.lastname@example.org for further details on submitting valid MFiT products.
For more information, see iTunes’ own Mastered for iTunes page.