Arriving bereft of ideas, Pink Floyd did something that was becoming increasingly rare on Meddle: They collaborated together in the studio.

At first, this didn't lead to much. The album, before its arrival on Oct. 31, 1971, was actually known as Nothing, Parts 1-24. Recorded in a series of locales around London between concert dates, Meddle eventually came together with help – both instrumentally and lyrically – from all four members, a stark contrast to the Roger Waters-dominated albums to come in the '70s.

"When we started on Meddle, we went into it with a very different working basis to any previous album in so much that we went into the studios with nothing prepared, and did a month of – well, we just called them nothings," Nick Mason told Ted Alvy of KPPC-FM in 1971. "I mean, they were ideas that were put down extremely roughly. They might have been just a few chords, or they might have been a rhythm idea, or something else – and this was just put down, and then we took a month and examined what we got."

What emerged was the bridge between their earliest recordings and the career-making triumph of 1973's The Dark Side of the Moon. Meddle still boasted the wide-open improvisational gumption of transitional albums like 1968’s A Saucerful of Secrets, 1969's Ummagumma and 1970's Atom Heart Mother, but their focus started to narrow. In some ways, the LP represents the best of both worlds.

They got there together, swapping musical ideas and – in the case of the album-opening "One of These Days" – even swapping places. David Gilmour took up the bass as the song opens, before being joined by Waters. (You'll notice the second double-tracked instrument has a flatter sound. "We didn't have a spare set of strings for the spare bass guitar, so the second bass is very dull sounding," Gilmour told Guitar World in 1993. "We sent a roadie out to buy some strings, but he wandered off to see his girlfriend instead.") Mason takes a rare vocal turn on "One of These Days," as well.

A swirling breeze links that song to the tender "A Pillow of Winds," which was inspired by time spent by Waters and Mason with their wives in the south of France. Waters' "San Tropez" – the only song here not co-written with Gilmour – also recalls trips to the French Riviera. Together, Pink Floyd bring an impish humor to songs like "Fearless," which features a field recording of a Liverpool soccer club singing "You'll Never Walk Alone" – forcing Pink Floyd to co-credit Rodgers and Hammerstein – while "Seamus" includes the howling of Small Faces/Humble Pie star Steve Marriott's dog, whom Gilmour was watching.

Listen to Pink Floyd Perform 'Fearless'

Meddle will always be defined, however, by its side two-encompassing closing track, "Echoes." The song, which stretched to 23 minutes, again grew out of a collaborative moment – this time onstage, when the song was reportedly introduced as "Return of the Son of Nothing."

Richard Wright wrote the long piano intro and the chord progression, while Waters added lyrics – after coming up with the idea of running Wright's original "ping" sound through a Leslie rotating speaker. Gilmour achieved the seagull sounds by reversing the inputs on a wah pedal.

"Things like 'Echoes' would be all of us in a rehearsal room, just sitting there thinking, playing – working out ideas to see if they went anywhere," Wright told Rolling Stone in 1987. "It's a nice way to work – and I think, in a way, the most 'Floyd-ian' material we ever did came about that way."

"Echoes," which later provided the title to a career-spanning retrospective, was Pink Floyd's breakthrough moment. An complex and stirring finale, "Echoes" holds together as one narrative piece, unlike the lengthy title track from Atom Heart Mother.

"I think 'Echoes' is the masterwork of the album – the one where we were all discovering what Pink Floyd is about," Gilmour told Guitar World. "Meddle is really the album where all four of us were finding our feet – the way we wanted Pink Floyd to be, much more than on Ummagumma or Atom Heart Mother. Although Atom Heart Mother has some pointers and directions as to where we would finally go, it's not as important as Meddle was."

Evn though Meddle reached No. 3 in the U.K., the U.S. was proving a tougher market to conquer. The album actually finished 15 spots further back from Atom Heart Mother, at a paltry No. 70. Still, the stage was set – as evidenced by the appearance in these sessions of "Brain Damage," which would later help close out The Dark Side of the Moon.

"All those stages are part of a general evolution, made of progression and dead times," Mason mused in 1973, as Pink Floyd found themselves finally on the cusp of superstardom. "They weren't exactly succeeding experiments, but rather exercises about a particular aspect of music, so you could evolve after that. Anyway, we never did an album saying, 'That's it, we reached the zenith.' On the contrary, we always asked ourselves: 'What will we do next?'"

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