When Eric Prydz released “Opus” in 2015 as the title track of his debut artist album, few expected a four-to-the-floor progressive house track to become a modern classical crossover phenomenon. The track, which builds from a gentle, melancholic arpeggio into a euphoric, string-laden explosion, is a masterclass in tension and release. For pianists, transcribing “Opus” is not just about playing notes; it is about capturing feeling .