Terry Riley, the American minimalist composer, received his most important inspiration 50 years ago on a San Francisco bus. He had just been in Europe working with the jazz trumpet player Chet Baker, and was searching for a way to fuse classical and jazz music that also allowed the musicians space to improvise. A note came into his head. A relatively uninteresting note: C. The note wouldn’t go away. It repeated over and over in his head.

He arrived home, and he composed In C, a work consisting of 53 constantly repeated short motifs based on the note that had enlivened his bus journey. The work made Riley famous, and it continues to be one of the most famous in the minimalist repertoire. “It gets more requests, more emails, than any other score I have ever written,” Riley told me a decade ago when I visited him in California.

Around the same time in the 1960s, the young Canadian singer-songwriter Joni Mitchell began busking in the streets of Toronto. Such was her distinctive high-pitched voice and unorthodox guitar tuning, not to mention an unusual degree of literary prowess, that she soon graduated to the city’s folk clubs. She moved fast: first Michigan, then New York, then southern California, setting standards of singer-songwriting that have yet to be equalled. Her fresh, early songs are among her best-known: the preternaturally mature “Both Sides Now”; the proto-ecological “Big Yellow Taxi” (“They paved paradise, and put up a parking lot”).

Terry Riley and Joni Mitchell, in their different ways, are heroic cultural figures of the 1960s. Riley, 79, continues occasionally to perform live. Mitchell, 71, doesn’t: she lives a relatively solitary life, prefers painting to singing, and suffers from Morgellons Disease. Now and again she says something spectacularly grumpy (see her famously dismissive recent remarks on Bob Dylan) which wakes up her fans. But both of these innovative artists are mostly remembered for past glories. And both have had to face the problem of how to be remembered, as they move further and further away from what is regarded as their creative peak.

This is a particular issue for artists of the pop era. It didn’t bother Beethoven. Nobody catcalled for him to play his earliest symphonies when he was in the last decade of his life. Instead, he wrote the late String Quartets, masterpieces of musical complexity that continued to revolutionise his art form. Artists then were allowed to grow old, and continue to refine their work. It was assumed that it would only become richer, wiser, more profound. Their very ageing was treated with respect.

But that luxury has never been afforded to artists of the pop age, who are expected to shine brilliantly for a short while and then negotiate their long-term decline in the public eye. It is a merciless trajectory. Elvis was essentially finished at 23. The audiences who today flock to see the affectionate Kinks musical Sunny Afternoon in the West End show little interest in hearing Ray Davies’s latest songs. Does anyone seriously expect any great, original work from Paul McCartney? Or Damien Hirst, for that matter, already adrift from his own golden age, the 1990s?

But great artists will never be content to surrender to ephemerality. They find new ways to visit their own past, and make it fresh all over again. And so, back to Terry and Joni. Last week saw the release of a new video performance of Riley’s In C, presented in a bold new format that actively seeks new audiences for the veteran composer. The film, made with the collaboration of Tate Modern, the musical collective Africa Express, and The Space, shows a group of African musicians tackling the work live at the gallery.

The interactive piece — you can choose how to view it — is interspersed with footage of the musicians in Mali, and also features works from the Tate’s collection of minimalist artists — Donald Judd, Josef Albers and Frank Stella. The result is an exemplary piece of cultural recycling. Riley composed the work to counter what he regarded as the unfeeling excesses of atonality and musical complication for its own sake. Now that battle has been largely won, In C finds new resonance in the more multi-layered musical landscape of the 21st century. It continues to live and breathe.

Not entirely unexpectedly, Mitchell has been more interventionist in the recasting of her past material. The release, also last week, of Love Has Many Faces, a four-CD box-set of some of her most affecting love songs, is described as a “curation” by the artist. The collection is subtitled: “A Quartet, A Ballet, Waiting to be Danced”, referencing its origin as a yet-to-be performed dance piece, and imbuing it with a structural integrity that is not found in your regular “greatest hits” mash-up.

Mitchell has remastered and resequenced her songs, gathering the various cinematic scenes described in them “like a documentary film-maker”. She tried, she says, to limit the collection to one disc to make the ballet, but was unable. “Quartets are nothing new in literature,” she adds spikily, “but for today’s abbreviated minds, this could be a challenge.” (Her regular fans should buy this set instantly, if only for her fluent and uncompromising essay.)

The four “acts” concern the various phases of love. The first three follow the ups and downs, while the final section, called “If You Want Me I’ll Be in the Bar”, settles into a kind of benign resignation. That is where we find the singer’s 2000 version of “Both Sides Now”, cracked-voiced and steeped in all the things that pop was never meant to understand: pathos, loss, and finally, acceptance.

peter.asden@ft.com, @peteraspden

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