Apple Music streams everything in 256kbps AAC . However, their Mastered for iTunes (now Apple Digital Masters) files for Dr. Dre are often 256kbps AAC sourced from 24-bit masters. Note: 256kbps AAC is mathematically transparent to 320kbps MP3. You don't need 320kbps AAC if it is an Apple Master; 256 is actually better than 320 MP3.