Is there another music critic writing today who could change key within an essay from John Dowland to Led Zeppelin (specifically, 'Dazed and Confused'), JS Bach to Robert Johnson, without fluffing the notes? Alex Ross of the New Yorker can span endless octaves of period and genre without the slightest sign of strain. Those particular leaps between Renaissance dance and song, and the pillars of hard rock, come in a bravura piece on the chaconne and its offshoot the lamento: a descending bass line "like a chilly staircase stretching out before one's feet". Such strands of musical DNA crop up as foundation and inspiration with a fertility that makes a nonsense of moribund divisions between the 'pop' and 'classical' traditions.

That vision of music and its makers as a single realm artificially split into warring camps drove Ross's superb book about the sound of the 20th century, The Rest is Noise. Here, he selects and adapts from more than a dozen years of New Yorker pieces. An initial manifesto voices with blazing eloquence his impatience with the class-bound fate of classical music in the west, "an ageless diva on a nonstop farewell tour". Later he quotes, in sympathy, Juilliard School drop-out Miles Davis's belief that "No white symphony orchestra was going to hire a little black motherfucker like me".

Instead, Ross imagines a future in which hard-core punks will hear Beethoven's 'Eroica' and discover the shock of the new in its convention-wrecking 200-year-old chords.

The book splits its attention between the living and the dead. Lavish New Yorker funding permits expansive on-the-road profiles of Radiohead, Bob Dylan and Björk.

With conductor-composer Esa-Pekka Salonen in Los Angeles, and pianist-teacher Mitsuko Uchida in Vermont, Ross enjoys the company of forward-thinking classical virtuosi who seek to escape their music's entanglement in "a web of money and status". After his podium debut in LA, Salonen slopes off to a club and gets talking to a woman at the bar. What had he been doing that night, she asks? "Well, I just conducted the LA Philharmonic." "That's the dumbest line I ever heard."

Ross spends perhaps too much time hanging out with favourite stars. The threat of fan-boy gush looms. "Like all greatly gifted people", Thom Yorke of Radiohead "is not always easy to be around". Yet when he listens to the music rather than the fame, his evocations sound pitch-perfect. The voice in early Björk burns "like candles in a dark room"; Schubert's Winterreise song cycle shares a "skeletal lyricism" with Samuel Beckett.

Ross ends not with a living legend but a heartfelt portrait of Johannes Brahms: the ultimate example of a composer scorned by the young but often adored once time begins to leave its mark. For Ross, the first 'Intermezzo Opus 117' is "the music you will hear when you die". Blessed is the critic who, like Ross, can stride so nimbly over the keyboard of time and style without losing his ear for the feeling behind the form.

Listen to this By Alex Ross, Fourth estate £25