Set the Controls

Barrett went his way with Jenner and King, and later recorded two haunting solo albums — on which Waters, Wright and especially Gilmour helped — before retreating to Cambridge for the rest of his life. The other four acquired a new manager — Steve O'Rourke — and in a state of some consternation finished their second album, A Saucerful of Secrets (begun the previous year).

Lyrical duties had now fallen to the bassist Roger Waters. And apart from 'Jugband Blues' — a disturbing track by Barrett, who contributed little else — the album's standout moments included the title track and Waters' 'Set the Controls for the Heart of the Sun'.

This hypnotic epic signposted the style the band would expand on in the Seventies, its vision at first more appreciated by an 'intellectual' and European audience. The Floyd played the first free concert in Hyde Park, and laid down the soundtrack for the bizarre Paul Jones movie vehicle, The Committee. They toured continually, developing new material on stage as well as in the studio.

And they worked on the experience, in April 1969 revealing an early form of surround-sound at the Royal Festival Hall — their rebuilt 'Azimuth Co-Ordinator'. (The prototype, first constructed and used in 1967, had been stolen.) They worked on their concepts, too - at that concert, performing two long pieces fusing old and new material, entitled 'The Man' and 'The Journey'.

So their star continued its inevitable ascent. In July, the Floyd released More, less a soundtrack than an accompaniment to Barbet Schroder's eponymous film about a group of hippies on the drug trail in Ibiza. The same month, they played live 'atmospherics' to the BBC's live coverage of the first moon landing. In November, they released the double-album Ummagumma, a mixture of live and studio tracks — and that same month reworked its outstanding number, the eerie 'Careful With That Axe, Eugene', for Antonioni's cult film Zabriskie Point.

With Ummagumma at Number Five in the UK charts, and a growing reputation in both Europe and the US underground, the Floyd played some of the key festivals of their time — Bath, Antibes, Rotterdam, Montreux — and between October 1970 and November 1971, put out two more albums.

Atom Heart Mother, their first Number One, featured the Floyd in their pomp — 'I like a bit of pomp,' says Gilmour (who also made his first lyrical contribution with the gentle 'Fat Old Sun'). And Meddle included two timeless and largely instrumental tracks that showcased their lead guitarist in all his vertiginous, keening glory: 'Echoes', which took up the whole of Side One and began with a single 'ping' created almost accidentally by Wright, and 'One of These Days'.

Increasingly successful, in 1972 the band was still pushing the boundaries. They shot the film 'Live at Pompei' in a Roman amphitheatre, recorded another movie soundtrack for Schroder — Obscured by Clouds — and performed with the Ballet de Marseille. But more importantly, they began to work on an idea that would become their most popular album and with 45 million sold, the world's third biggest.

Provisionally entitled 'Eclipse' and honed through an extensive world tour, The Dark Side of the Moon was released in March 1973, and defies a potted critique here. Demonstrating Waters' talents as both lyricist and conceptualist, it was also a musical tour de force by Gilmour. But Waters was becoming de facto leader of the band — which in public at least was becoming less about the individuals than the experience.

That was (as Barrett had always intended) increasingly visual. The intriguing sleeve artwork commissioned from the ex-Cambridge outfit Hipgnosis was complemented by stage shows featuring crashing aeroplanes, circular projection screens and flaming gongs. There were backing singers on-stage and a guest slot for another pal from Cambridge, the saxophonist Dick Parry. In the dawning age of stadium rock, the Floyd were truly its masters.

Or maybe its servants? Even before Dark Side broke Middle America through FM radio — with the single 'Money' — alienation, isolation and mental fragility had long been Waters' themes. As a stadium performer, and a cog in the music business machine, he was becoming more prone to all three. As Barrett's ex-colleague, he had seen them embodied in his old friend. The results were evident in two of his best lyrics — for 'Shine On, You Crazy Diamond' and 'Wish You Were Here'. These tracks were the high points of the Floyd's next LP, also called Wish You Were Here, which was begun in January 1975 and released that summer.

Famously, Barrett briefly appeared unannounced at Abbey Road during the recording of 'Shine On' and shocked the band by his appearance and demeanour. It was the last time any of them saw him — but they were seeing less of each other, too. Personal and musical differences were starting to tell on the band, though it would be several years until these became unbearable — and two more LPs.