A striking moment occurs midway through the opening movement of the Hungarian composer Gyorgy Ligeti’s 1970 Chamber Concerto. After spinning a dissonant web of melodic strands in the opening minutes, the instruments arrive at that most fundamental of intervals: the perfect octave. Time is momentarily suspended.

But a dense tone cluster of brass and Hammond organ interrupts this repose, and the music devolves into a buzzing, asynchronous mass.

For audiences accustomed to Tchaikovsky’s lyricism and Mozart’s familiar harmonies, this music borders on incomprehensibility. Even as some of their works are almost a century old, modernists like Ligeti, Pierre Boulez, and Ruth Crawford Seeger still pose a challenge. What are you supposed to pay attention to? How should you listen to this stuff?