Book copyright is pretty straightforward - text is produced by an individual, who usually retins copyright for it. Recording music is a more complex scenario, involving advances from record companies to finance studio time, and songwriting and performing royalties. Record companies do not always retain copyright - it's a complex system of contracts worked out with the company and artist - it boils down to the bigger the artist, the more copyright control they tend to get, but there are many and various ways of coming to that conclusion.