it goes.

Then Trey Anastasio begins to sing. And suddenly, with whiplash force, the new vistas vanish and we're yanked back into the phantasmagoric world of Phishspeak, circa 1995 -- that shadowy realm where everything has triple meanings and the words are too cumbersome for the elegant music that carries them. It's all here: Tom Robbins-ish non sequiturs, ostentatious pronouncements, Zen riddles. "Pebbles and marbles like words from a friend," sings Anastasio in a coarse voice that often strays from the pitch. "Make us hold tight but are lost in the end." Oh, the heaviosity!

Anastasio, ever the soldier, rides the conceit of "Pebbles and Marbles," all the while sounding like he's determined to break through to something better. He grinds out ferocious double-time rhythm-guitar chords as he leans into the song's hook, and by the halfway point he's wound the thing up to a full gallop and it's interesting again. Though the vocals reappear from time to time, the song's second half is mostly instrumental, and it's a journey markedly different from the frictionless guitar-star hyperglide that made some Phish shows seem perfunctory. This time, nobody sits at center stage -- Anastasio tosses out some melodies, but he's also cultivating dark, droning chords that ooze menacingly in the background. McConnell -- once Mr. Unobtrusive -- jabs and thrashes and pounds out frightening chords that have a freakish bipolar character -- Keith Emerson coming through one hand, Thelonious Monk the other.

There are five extended adventures on Round Room, and while they're each unique compositionally, all of them are compelling for the same reason: These guys are actually listening and responding to one another. Gone is the cruise-control comportment of their occasional bad gigs, their overreliance on a riveting groove. In its place is the collective pursuit of upheaval: After spending two years doing other things, playing music in un-Phishlike settings, the four musicians appear newly dedicated to changing the very temperature of their interactions. They're baiting one another, throwing down challenges, chasing gnarled conversations that don't resolve neatly, looking for new levels of engagement. Their exchanges transform the ordinary organ-funk pulse of "46 Days" into a lacerating workout, elevate "Seven Below" to a sublime, impossibly fluid rhythm, and are at the heart of the cresting peaks that define "Wav