To listen to Philip Glass’ 20 piano etudes is to be taken on a far-reaching journey, as he explores not just his entire stylistic spectrum, but his deep love of the great composers, too. Some of these pieces are, naturally, pure Glass—Etude no. 17 is a gently undulating miniature in the mold of his hit soundtrack to the film The Hours. But Etude no. 1 evokes Beethoven’s melodic inspiration and Etude no. 15’s exotic, Impressionist harmonies recall Debussy’s chiming piano masterpieces. Etude no. 9, meanwhile, is a simple piece of improvisation that’s poignant in its harmonic stasis.