Released 40 years ago this month and officially the fastest-selling single in American music history, USA For Africa’s ‘We Are The World’ shifted over 20 million copies and raised a huge amount of money for African famine relief.

Co-written by Michael Jackson and Lionel Richie during a few sessions at the former’s house in Encino, the song divides opinion but only the hardest heart could fail to be moved by its recording (even if one can definitely feel the vibe of some major agent/star power – no arriving in the manager’s battered old car for this lot…).

It brought together a fairly astonishing cast list of the great and good. And, inadvertently, it also arguably represented a last gasp for classic 1980s R’n’B and yacht rock.

The basic track was recorded at Kenny Rogers’ Lion Share Studios on 22 January 1985 with king-of-the-cross-stick John ‘JR’ Robinson on drums, bassist Louis Johnson and pianist Greg Phillinganes, closely monitored by a huge press corps, co-producers Quincy Jones and Michael Omartian and engineer Humberto Gatica. According to Robinson, all the musicians were sight-reading a chart and a click track was used, and they didn’t do more than two takes.

A few days later, Lionel sat down with Quincy and vocal arranger Tom Bahler to prep who would sing which lines (the decision was also made to mainly record vocals live and ‘in the round’ with no or at least very few ‘punch-ins’, unlike ‘Do They Know It’s Christmas’). All the major vocalists were then sent a copy of the basic track featuring Jackson’s guide vocal and with an enclosed letter from Lionel.

The featured singers then assembled at A&M Studios at around 9pm on Monday 28 January, most arriving after the American Music Awards (which Richie hosted). Notable absentees: Madonna (who was apparently bumped in favour of Cyndi Lauper), Prince (check out Duane Tudahl’s superb book for the details), George Benson, Dolly Parton, Donna Summer, Michael McDonald, Pat Benatar, Rod Temperton, Stevie Nicks, Joni Mitchell, Billy Idol? And is it odd that Smokey Robinson didn’t sing a solo line?

The complete footage of the recording session is still fascinating. We see how some of the biggest names in music history found different ways of preparing. Steve Perry waits for his line with eyes shut, looking down, listening intently. Diana Ross does just the opposite.

Bob Geldof gives a stirring pep talk and Stevie Wonder brings in two Ethiopian women to address the singers, moving many to tears. It’s hard not to be touched by Stevie, Kenny Rogers, Dionne Warwick, Diana, Steve Perry, Ray Charles and Cyndi Lauper’s vocals. But Harry Belafonte, Ray Charles, Bob Dylan and Bruce Springsteen seem to get the most respect from the assembled stars.

Other observations: Brucie – who had finished the latest leg of the Born In The USA tour the night before – looking like Judd Nelson in ‘The Breakfast Club’. Al Jarreau struggling throughout. Lionel the team player. Stevie giggling like a naughty schoolkid when Quincy gets annoyed. James Ingram hiding behind Kenny Rogers after a boo-boo.

Paul Simon twice saying to Rogers: ‘Can I help?’ Lauper sharing vocal tips with Kim Carnes. MJ holding hands with Diana and Stevie. Quincy and Stevie rehearsing with Bob Dylan. Stevie and Ray Charles using their braille machine. Quincy reading the score as he conducts the soloists, and his witty asides: ‘Who you gonna call?’ etc.

It looks like they recorded the first half of the song first (up to and including Daryl Hall) and then spent some time on the middle eight with Huey Lewis, Lauper and Carnes.

How does it sound now? Phillinganes’ piano playing is a pleasure to hear, typically tasty and gospel-inflected. But the track is inundated with synths – no less than four players are credited, including David Paich and Steve Porcaro from Toto – and probably why it reminded many of a Pepsi ad.

And it’s odd that the song features no guitar, though Prince offered to play a solo – Quincy reportedly told Prince’s manager Bob Cavallo: ‘I don’t need him to play guitar, we got f*ckin’ guitars’!