Original: Towards the end of the 15th century, polyphonic sacred music (as exemplified in the masses of Johannes Ockeghem and Jacob Obrecht) had once again become more complex, in a manner that can perhaps be seen as correlating to the stunning detail in the painting at the time.
Simplified: Towards the end of the 15th century a style of polyphonic sacred music had been developed that can be heard in the masses of Johannes Ockeghem and Jacob Obrecht.