I was extremely interested to note that pianist Andras Schiff is appearing at this year's Festival where, in the Usher Hall, he'll play a mixed programme of sonatas by Beethoven, Bartok, Janacek and Schubert.

This column has absolutely nothing to do with that concert a week on Monday, other than there is a Beethoven element in both. Principally, the column is connected with a double recording Schiff made just under a year ago, featuring two performances, each on a different instrument of a different period, of Beethoven's colossal opus 120 piano work, the so-called Diabelli Variations.

There are many fascinating stories about this piece, not least about big-name, legendary pianists who refused to play it because it was too intimidating and even unwieldy. Another pianist, not a big name, whom I met many years ago, said he wouldn't touch it because he felt, ultimately, it lacked gravitas and was "a bit of a joke". In a way it is: Paul Griffiths, a doyen among analysts, wrote, spot on the mark, as he often is: "The wonder of the Diabelli Variations is the wonder of superlative absurdity." And that statement, at its most literal, provokes some thought about how Beethoven produced, from one of the silliest, most banal and piffling little tunes ever tossed off, a staggering, multi-layered, multi-faceted masterpiece that is simultaneously as playful as it is transcendent, and as comically witty as it is, cumulatively, Olympian. It's daft and divine, both at the same time.

But for the best story about Beethoven's 32 Variations On A Waltz By Diabelli, to give it its Sunday name, we have to turn to Mr Diabelli himself. Anton Diabelli was an Austrian music publisher who, with a business partner, set up his firm in Vienna in 1818. He was a shrewd operator, plugging in to the fashionable demands for publication of operatic and dance music. He was also alert to musical potential: he it was who spotted, championed and published the music of Schubert.

But his real coup, establishing his name in the history books, was a brainwave in 1819, which was at once a marketing stunt and a clever business initiative. Diabelli composed a rudimentary little waltz theme: cheap, cheerful, catchy and engaging. He then sent it to every notable and significant figure in musical Vienna, inviting them each to compose and contribute a single short variation on that tune. His intention was, in a pure business initiative, to take their offerings and bind them together into a single glossy publication which he would then sell through his publishing business, increasing the kudos of his company as well as its profits.

They all took the bait, and some 50 contributions came from as diverse sources as the big names of the day, including Hummel (of Trumpet Concerto fame) and Moscheles, from Archduke Rudolf of Austria to an eight-year-old Franz Liszt, encouraged into it by his teacher Carl Czerny, author of the famous studies and exercises which, to this day, have music students tearing out their hair. Czerny himself contributed the coda to Diabelli's "collection".

That Beethoven even entertained the notion of obliging Diabelli with a variation, never mind doing what he did, remains a curious conundrum to me. After all, Beethoven was deep into his last period and late works: he was up to the eyes in writing the mighty and majestic Missa Solemnis, and he was about to write the overwhelming final piano sonatas.

That he didn't just brusquely and dismissively sweep aside Diabelli's paltry little waltz is intriguing. Yet not only did Beethoven undertake and indeed take over the waltz tune to produce his own, cohesive, encyclopedic and mind-blowing set of 32 Variations: he actually interrupted and set aside the composition of the Missa Solemnis to do it. Twice.

Something in Diabelli's little ditty ignited Beethoven's visionary imagination, resulting in one of the greatest keyboard works of all time. For anyone interested in the other contributions to Diabelli's volume, they are all annotated online now along with recommended recordings.