How does one of rock history's most influential acts sign off?

For Pink Floyd, it will be with a collection of outtakes bearing the band's epic psychedelic roots -- but whose theme this time is not alienation, but continuity.

Pink Floyd has declared that "The Endless River" -- the band's first album in 20 years -- will be the finale for the Cambridge, England group whose dark, sonic landscapes transformed personal isolation into stadium-filling rock.

"The Endless River," which will be released between Friday and Tuesday around the world, has been one of the year's most anticipated releases and has topped pre-order charts.

But the band that showed outsized conceptual vision on albums such as "Dark Side of the Moon" and "The Wall" did not attempt a last magnum opus and instead dusted off unreleased material from 1994's "The Division Bell."

"The Endless River" is mostly an instrumental affair except for the final track, "Louder than Words," whose lyrics and flowing guitar match the album's cover art of a solitary boatman paddling into the sunset.

"With world-weary grace / We've taken our places," David Gilmour sings, in lyrics written by his novelist wife Polly Samson. "It's louder than words / This thing that we do."

Music in 'right mood'

Another non-instrumental track, "Talkin' Hawkin'," features guest vocalist Stephen Hawking, the Cambridge University physicist who speaks with a computerized voice due to amyotrophic lateral sclerosis and also featured on "The Division Bell."

Keyboardist Richard Wright, who died in 2008, wrote much of the music. The album opens with a tribute in the form of "Things Left Unsaid," an aptly instrumental work consisting of just a mournful keyboard.

Gilmour's guitar and Nick Mason's drums kick in on the second song, "It's What We Do." The nearly hour-long album then flows the course of the river through calm currents on "Ebb and Flow" and the more violent waters on "Sum" and "Allons-y."

"You have to get into the right mood to listen to this," said Gilmour, who has been a critic of the rapid skipping among tracks that is increasingly commonplace in the era of instant online music.

"There are lots of people who still love listening to music that way -- listen to the whole thing, a whole piece, all the way through," he said in a video message released ahead of the album.

Gilmour and Mason spent two years on the album, originally trying to stay pure to the posthumous recordings of Wright but eventually expanding on them at the band's Britannia Row Studios in London.

"There are ideas there that actually almost can be seen in some of the really early albums, in terms of assembly of music that is not in regular song format," Mason said.

Pink Floyd's two remaining members both said that they believed Wright would have appreciated the end product.

"It's very evocative and emotional in a lot of moments," Gilmour said. "This is the last chance anyone will get to hear him just playing along with us."

Only two members left

While the band tried to preserve Wright's legacy, Roger Waters -- the driving force behind "The Wall" -- played no role in Pink Floyd's final act.

Waters, known for his strong personality, dismissed questions about the album, noting that he left Pink Floyd in 1985.

"I have nothing to do with Endless River. Phew! This is not rocket science people, get a grip," he wrote on his Facebook page.

Pink Floyd's last album also does not include original lead singer and guitarist Syd Barrett, who died in 2006. Barrett left the band in 1969 as he struggled with mental illness -- which inspired the band thematically, particularly on the 1975 album "Wish You Were Here."

Gilmour, 68, recently told the BBC that Pink Floyd had no further material to record.

"It's a shame, but this is the end," he said.

But Mason, while deferring to Gilmour on the band being over, told Rolling Stone that he was still holding on to Pink Floyd.

"I now believe when I'm dead and buried my tombstone will read, 'I'm not entirely sure the band's over,'" Mason said.