It is a year of music anniversaries.

In June, it will be 50 years ago today when The Beatles released what some (wrongly) deem their signature album. The same month, Jimi Hendrix played Monterey. The definitive divorce album, Fleetwood Mac’s Rumours, marked its 40th in February. It’s 20 years in May from Radiohead’s OK Computer, dubbed for a while the greatest rock album of all time. Elvis left the building for the final time in August 1977.

What is absent from the above list is an album which arguable dwarves the lot, even though its creator was 5’ 2”. It combines all the aspects of the previous work. A frontman who reinvented the live game, with as many comebacks as Elvis, who shredded and picked like Hendrix, wrote a barrowload of hits, recounted all his messy relationship details in song and performed a purple patch of music in four years to rival The Beatles’ imperial phase of Rubber Soul, Revolver, Sgt. Pepper and The White Album.

For those not following, the clue was in the word “purple”.

Prince’s masterpiece Sign O’ The Times was released 30 years ago today.

Some fans prefer the quirkier Parade, the mainstream audience cleaves Purple Rain closer to its heart, and Diamonds and Pearls sold three times more in the UK. If, however, you want a case study on occasions when the word genius is not always overused in music criticism, Sign O’ The Times is the occasion.

It’s special because classic albums are the result of a band or solo act relying on a producer in sync with their moods and talents.

Even a solo confessional like Carole King’s Tapestry benefitted from Lou Adler’s production.

So much of Sign… is his work alone. The daring of a man who should choose to file for divorce from most of his band after a flop movie and embark on making a triple album – Crystal Ball would become Sign O’ The Times – is breathtaking.

In some respects, Prince was fixated with concept albums through his imperial phase. Purple Rain in 1984 was the result of “60 or 70 songs written for the movie” his keyboard player Matt Fink told me for a BBC feature on the album. The intention on 1985’s Around the World In A Day was to create a psychedelic Beatles-esque landscape and in 1986 Under the Cherry Moon and its soundtrack Parade aimed for a South of France 1920s playboy feel. By 1987, Sign O’ The Times had its own concept. That concept was Prince.

On October 7th 1986, Prince broke up his band, The Revolution. On October 8th, the post-revolution era started with the home recording of Housequake. A voice sped up and slowed down, horns featuring Eric Leeds’ sax, who told me it was done “in an hour”, and a drum beat programmed himself to create a splash of pop-funk which doesn’t sound like that or any other era.

He even stuck on some applause at the end. It’s merited.

Sign O’ The Times criss-crosses the genres of soul, funk, rock, Top 10 pop, electronica, acoustic confessional and the plain weird.

The lyrics are by turns searing, sensual, spiritual, soulful, sweet and silly. (“Shut up, already…damn” will mean nothing to some music fans, and everything to others. See also “Ooh, doggies!” and “Here we are folks, the dream we all dream of, boy vs girl in the world series of love.”)

The record is the sound of an artist zeroing in on what he’s good at and having fun. Mainly, it’s a man playing not just his guitar (which he does exquisitely), but with songs’ tempo and rhythm, with his gender identity on If I Was Your Girlfriend, with the idea of nursery rhymes on Starfish and Coffee. It isn’t just anyone who can persuade a talent show singer from Bellshill, North Lanarkshire discovered by Esther Rantzen, to sing “Sho’ nuff do be cooking in my book” on U Got the Look. Sheena Easton does this for Prince.

The Ballad of Dorothy Parker’s dark tone was the result of a studio mistake from cables missing from equipment shipped to his home studio which turned into a happy accident. He was clever enough to keep it.

Like one of his heroes Miles Davis, Prince plays in the spaces and leaves gaps. Much fuss was made of When Doves Cry from Purple Rain having no bass but there are similar moments here.

He ran freely and no one – not in the charts, nor his band, nor anyone since – could keep up.

Usually the thought of a nine-minute song on a double album would alert the listener to impending self-importance or self-indulgence. It’s Gonna Be A Beautiful Night is a nine-minute joyride. Meticulously recorded live in Paris and then re-recorded in the studio where Eric Leeds and Atlanta Bliss sounds as drilled as the marine corps under the bandleader’s instruction. No other popular musician in history could legitimately be mentioned in the same bracket as Duke Ellington, Jimi Hendrix, James Brown and even Mozart. Prince routinely is.

1987 was the year Quincy Jones asked Prince to duet on Michael Jackson’s big comeback single (opening line “Your butt is mine”) after Thriller.

Prince passed.

He was instead programming the drums, playing the guitar, screwing around with his vovals in the writing and recording of Sign O’ The Times. Lyrics for the title track, which would be covered by Nina Simone, Chaka Khan and Simple Minds, took in AIDS, the space programme, drugs, guns with gangs and mothers unable to feed their children.

Who’s Bad?

Listen to Sign O’ The Times. Argument settled.