Ask the question. Ask just exactly what is Ambient and David Toop will spend an entire book acquainting you. Yes, there is an introduction to this densely rendered, fascinating text, but the introduction is simply the first part of what is in essence a book-long introduction: the definition of Ambient is, he tells us, its place and its history.

That, if anything, is the best soundbite illustration: Ambient is about environment. From his brilliant summing-up:
With massive volume and density, categories barely matter... Music is felt at its vibrational level, permeating every cell, shaking every bone, derailing the conscious analytical mind.
Yes, Toop is saying, we can all identify the movement Brian Eno created (or identified and named: Ambient is omnipresent, of course), the records The Orb went on to make, but anything - even the terrifyingly discordant Free-jazz mastery of Peter Broztmann's 'Machine Gun' - is Ambient in context.

From its definition in the early seventies, Toop - himself a musician and journalist - traces roots back to 'world' music (whatever that now means) through a hundred years to classical progenitors like Debussy and, especially, Eric Satie, and on to the fathers of contemporary experimentalism, John Cage, Terry Riley and La Monte Young. He is particularly good on Cage's classically misunderstood 4'33", often called 'Silence' because it revolves around a musician deliberately not playing their instrument. The subject of ridicule or Zen-like reverence, Toop rightfully reclaims the work as a nascent Ambient masterwork, identifying the 'subtle awareness of the silence which surrounds sounds'.

Much space is devoted to the other two key elements of form in this shifting textural sea - this ocean of sound: Jazz and Dub. Charlie Parker, the late and decidedly great Sun Ra (interviewed), Ornette Coleman, and especially John Coltrane all merit discussion from the former camp; King Tubby, Prince Far-I, Augustus Pablo, and the cherishable Lee Perry (also intelligently, interviewed) from the latter. The point is made: Jazz and Dub, musics so obviously of place, are Ambient's catalysts.

Talking about Ambient (or ambient?) and not talking about Brian Eno is like discussing World War II without mentioning Adolf Hitler. The story of his invention is in here again, if you want it; an auspicious collision of circumstance and susceptibility. But more than that, Eno has been the one to fully appreciate Ambient's method and implication, the capacity of a music that can exist without being heard. Music For Airports, Thursday Afternoon, obviously, but maybe even more so the extraordinarily ephemeral Neroli, or his production of Bryars' outstanding docu-poem The Sinking of The Titanic.

All of this is organised in an ocean-cruise of ideas. This is no formal history, its author favouring an almost random - ambient - travel. Dream, fiction (Ballard is cited early), and thought mingle with documented fact and recorded interview in this gigantic patchwork. It's no ease read, as demanding on its audience's attentions as it's reliant on them at least knowing something of what's brought under discussion. (There is, inevitably, a double CD companion.)

Along with Reynolds/Press' astonishing gender deconstruction The Sex Revolts and Jon Savage's England's Dreaming, Ocean of Sound is arguably one of the most important books about music (limiting the definition) to be published in the last five years.